SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 13D

(RULE 13d-101)

INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE

13D-1(a)

AND AMENDMENTS THERETO FILED PURSUANT TO RULE 13D-2(a)

(AMENDMENT NO. 2)

TECHTARGET, INC.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

87874R 10 0

(CUSIP Number)

Frederic D. Fenton

c/o Technology Crossover Ventures

528 Ramona Street

Palo Alto, California 94301

(650) 614-8200

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 13, 2014

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition which is the subject of this Schedule 13D, and is filing this statement because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box  ¨.

(Continued on following pages)

EXPLANATORY NOTE

This Amendment No. 2 to Schedule 13D amends and supplements the statement on Schedule 13D originally filed with the Securities and Exchange Commission on June 1, 2007 and Amendment No. 1 to the Schedule 13D filed with the Securities and Exchange Commission on October 30, 2013 (collectively, the “Schedule 13D”), with respect to shares of common stock, par value $0.001 per share (the “Common Stock”), of TechTarget, Inc., a Delaware corporation (“TechTarget” or the “Company”). The Company’s principal executive offices are located at 275 Grove Street, Newton, Massachusetts 02446. Unless otherwise indicated, each capitalized term used but not otherwise defined herein shall have the meaning assigned to such term in the Schedule 13D. From and after the date hereof, all references in the Schedule 13D to the Schedule 13D or terms of similar import shall be deemed to refer to the Schedule 13D as amended and supplemented hereby.

This statement is being filed by (1) TCV V, L.P., a Delaware limited partnership (“TCV V”), (2) TCV Member Fund, L.P., a Cayman Islands exempted limited partnership (“Member Fund”), (3) Technology Crossover Management V, L.L.C., a Delaware limited liability company (“Management V”), (4) TCV Management 2004, L.L.C., a Delaware limited liability company (“TCM 2004”), (5) Jay C. Hoag (“Mr. Hoag”), (6) Richard H. Kimball (“Mr. Kimball”), (7) John L. Drew (“Mr. Drew”), and (8) Jon Q. Reynolds Jr. (“Mr. Reynolds”) (Mr. Hoag, Mr. Kimball, Mr. Drew and Mr. Reynolds are collectively referred to as the “Members”). TCV V, Member Fund, Management V, TCM 2004 and the Members are sometimes collectively referred to herein as the “Reporting Persons.”

This amendment is filed by the Reporting Persons in accordance with Rule 13d-2 of the Securities Exchange Act of 1934, as amended, and refers only to information that has materially changed since the filing of Amendment No. 1 to Schedule 13D. The items identified below, or the particular paragraphs of such items which are identified below, are amended as set forth below. Unless otherwise indicated, all capitalized terms used and not defined herein have the respective meanings assigned to them in the Schedule 13D.

Item 4 of the Schedule 13D is amended and supplemented by adding the following information to Item 4:

On May 13, 2014, TCV V, Member Fund, TCM 2004 and Mr. Hoag (together, the “Lock-Up Parties”) entered into a Lock-Up Agreement in the form attached hereto as Exhibit A (the “Lock-Up Agreement”) with Jefferies LLC, as representatives of the several underwriters (collectively, the “Underwriters”) of the Company in connection with that certain preliminary prospectus supplement (“Prospectus”) filed with the Securities and Exchange Commission on May 13, 2014, in which TCV V and Member Fund are named as selling stockholders. Pursuant to the Lock-Up Agreement, each of the Lock-Up Parties agreed, subject to certain exceptions, not to sell, transfer or dispose of, directly or indirectly, any shares of Common Stock of the Company or any securities convertible into or exercisable or exchangeable for shares of Common Stock of the Company, without prior written consent of Jefferies LLC, for a period beginning on the effective date of the Lock-Up Agreement and continuing through the close of trading on the date that is 75 days after the date of the Prospectus. The foregoing description of the terms of the Lock-Up Agreement is intended as a summary only and is qualified in its entirety by reference to the form of Lock-Up Agreement, which is filed as Exhibit A to this Amendment No. 2 and incorporated herein by reference.

(a), (b). As of the close of business on May 13, 2014, TCV V, Member Fund, Management V, TCM 2004 and the Members owned, directly and indirectly, (including shares issuable upon the exercise of options exercisable within 60 days after May 13, 2014) an aggregate of 10,531,288 shares of the Issuer’s common stock as follows:

Each of TCV V, Member Fund, and TCM 2004 (collectively, the “TCV Entities”) has the sole power to dispose or direct the disposition of the shares which it holds directly, and has the sole power to vote or direct the voting of its respective shares held by such TCV Entity.

Management V, as a general partner of TCV V and a general partner of the Member Fund, may also be deemed to have the sole power to dispose or direct the disposition of the shares and held by TCV V and Member Fund and have the sole power to direct the vote of such shares. Management V disclaims beneficial ownership of the securities owned by TCV V and Member Fund except to the extent of its pecuniary interest therein.

Each of the Members is a Class A member of Management V and a member of TCM 2004. Under the operating agreement of Management V, the Members have the shared power to dispose or direct the disposition of the shares held by TCV V and Member Fund and the shared power to direct the vote of such shares. Under the operating agreement of TCM 2004, the Members have the shared power to dispose or direct the disposition of the shares held by TCM 2004 and the shared power to direct the vote of such shares. Each of the Members disclaims beneficial ownership of the securities owned by TCV V, Member Fund and TCM 2004 except to the extent of their pecuniary interest therein.

The Reporting Persons may be deemed to be acting as a group in relation to their respective holdings in the Company but do not affirm the existence of any such group.

Securities that may be beneficially acquired within 60 days of May 13, 2014, including shares subject to options exercisable within 60 days of May 13, 2014 are deemed to be beneficially owned by the person or entity holding such securities for the purpose of computing ownership of such person or entity, but are not treated as outstanding for the purpose of computing the ownership of any other person or entity.

Except as set forth in this Item 5(a) - (b), each of the Reporting Persons disclaims beneficial ownership of any Common Stock owned beneficially or of record by any other Reporting Person.

The summary of certain provisions of the Lock-Up Agreement set forth in Item hereof 4 and the Lock-Up Agreement attached as Exhibit A are hereby incorporated by reference.

The following additional exhibits were filed:

SIGNATURE

After reasonable inquiry and to the best of each of the undersigned’s knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: May 16, 2014

TECHNOLOGY CROSSOVER MANAGEMENT V, L.L.C.

EXHIBIT INDEX

Exhibit A

Lock-up Agreement

May 13, 2014

Jefferies LLC

As Representative of the Several Underwriters

c/o Jefferies LLC

520 Madison Avenue

New York, New York 10022

Ladies & Gentlemen:

The undersigned is an owner of shares of common stock, par value $.001 per share, of the Company (“Shares”) or of securities convertible into or exchangeable or exercisable for Shares. The Company proposes to conduct a public offering of Shares (the “Offering”) for which Jefferies LLC (“Jefferies”) will act as the representative of the underwriters. The undersigned recognizes that the Offering will benefit each of the Company, the selling stockholders named in the Underwriting Agreement (the “Selling Stockholders”) and the undersigned. The undersigned acknowledges that the underwriters are relying on the representations and agreements of the undersigned contained in this letter agreement in conducting the Offering and, at a subsequent date, in entering into an underwriting agreement (the “Underwriting Agreement”) and other underwriting arrangements with the Company and the Selling Stockholders with respect to the Offering.

Annex A sets forth definitions for capitalized terms used in this letter agreement that are not defined in the body of this agreement. Those definitions are a part of this agreement.

In consideration of the foregoing, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the undersigned hereby agrees that, during the Lock-up Period, the undersigned will not (and, if the undersigned is an individual, will cause any Family Member not to), without the prior written consent of Jefferies, which may withhold its consent in its sole discretion:

The foregoing will not apply to the registration of the offer and sale of the Shares, and the sale of the Shares to the underwriters, in each case as contemplated by the Underwriting Agreement. In addition, notwithstanding the foregoing restrictions, the undersigned may:

(a) transfer Shares and/or Related Securities:

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(i) as a bona fide gift or gifts, in each case, that are made exclusively between and among the undersigned or, if the undersigned is an individual, the undersigned’s Family Members, or affiliates of the undersigned, including its partners (if a partnership) or members (if a limited liability company), or, in the case of gifts, that are made for charitable purposes;

(ii) to any trust for the direct or indirect benefit of the undersigned or, if the undersigned is an individual, any Family Member(s) of the undersigned, or if the undersigned is a trust, to any beneficiary (including such beneficiary’s estate) of the undersigned, provided that any such transfer shall not involve a disposition for value;

(iii) if the undersigned is a corporation, partnership, limited liability company, trust or other business entity, (A) to another corporation, partnership, limited liability company, trust or other business entity that is an affiliate (as defined in Rule 405 promulgated under the Securities Act) of the undersigned (including a fund managed by the same manager or managing member or general partner or management company or by an entity controlling, controlled by or under common control with such manager or managing member or general partner or management company as the undersigned or who shares a common investment advisor or common investment management with the undersigned) or (B) as part of a distribution without consideration by the undersigned to its current or former stockholders, partners, members or other equity holders, provided that in the case of any transfer pursuant to (A) or (B) above, it shall be a condition to such transfer that such transfer shall not involve a disposition for value;

(iv) if the undersigned is an individual, by will or intestate succession upon the death of the undersigned, provided that the transferee agrees to be bound in writing by the restrictions set forth herein;

(v) in connection with the “net” or “cashless” exercise or settlement of any warrants or of any stock options or any other equity awards granted pursuant to the Company’s 2007 Stock Option and Incentive Plan or any other plan, agreement or instrument existing on the date of this agreement, provided that any such Shares received upon such exercise or vesting shall be subject to the terms of this letter agreement; or

(vi) with the prior written consent of Jefferies;

(b) exercise any stock options granted pursuant to the Company’s equity incentive plans or warrants to purchase Shares, so long as the Shares received upon such exercise shall remain subject to the terms of this lock-up agreement;

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In the case of any transfer pursuant to clause (a) of the previous paragraph, it shall be a condition to such transfer that:

The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of Shares or Related Securities held by the undersigned or, if the undersigned is an individual, the undersigned’s Family Members, if any, except in compliance with the foregoing restrictions.

The undersigned confirms that the undersigned has not, and, if the undersigned is an individual, has no knowledge that any Family Member has, directly or indirectly, taken any action designed to or that might reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale of the Shares. The undersigned will not, and, if the undersigned is an individual, will cause any Family Member not to take, directly or indirectly, any such action.

Whether or not the Offering occurs as currently contemplated or at all depends on market conditions and other factors. The Offering will only be made pursuant to the Underwriting Agreement, the terms of which are subject to negotiation between the Company, the Selling Stockholders and you.

In the event that Jefferies (the “Releasing Party”) consents to the exclusion, release or waiver of any Shares or Related Securities held by a stockholder of the Company from the foregoing restrictions, the Releasing Party shall notify the Company and the Company will give the undersigned notice of such release, stating the percentage of such stockholder’s Shares released from the foregoing restrictions, and the same percentage of Shares or Related Securities held by the undersigned shall be released from the foregoing restrictions concurrently therewith; provided, however, that if such release is in response to a request from the Company’s management team to partially release a total of three (3) or fewer stockholders from the foregoing restrictions for a number of such securities whose aggregate value (measured as of the closing price on the day before the release occurs) is not more than $100,000, and such release is requested in response to a financial hardship for which such stockholders have no other reasonably available sources of liquidity, then no notice of such release is required, and no Shares or Related Securities held by the undersigned shall be released from the foregoing restrictions. The provisions of this paragraph will not apply if (i) the release or waiver is effected solely to permit a transfer

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not for consideration and (ii) the transferee has agreed in writing to be bound by the same terms described in this agreement to the extend and for the duration that such terms remain in effect at the time of the transfer.

The undersigned hereby represents and warrants that the undersigned has full power, capacity and authority to enter into this letter agreement. This letter agreement is irrevocable and will be binding on the undersigned and the successors, heirs, personal representatives and assigns of the undersigned.

This letter agreement shall lapse and become null and void if (i) the Company notifies Jefferies in writing prior to the execution of the Underwriting Agreement that it does not intend to proceed with the Offering, (ii) the execution of the Underwriting Agreement has not occurred prior to June 30, 2014, or (iii) for any reason, the Underwriting Agreement is terminated prior to the closing of the Offering.

This letter agreement shall be governed by, and construed in accordance with, the laws of the State of New York, without regard to the conflict of laws principles thereof.

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[Signature Page to Lock-Up Agreement]

Certain Defined Terms

Used in Lock-up Agreement

For purposes of the letter agreement to which this Annex A is attached and of which it is made a part:

in each case whether effected directly or indirectly.

Capitalized terms not defined in this Annex A shall have the meanings given to them in the body of this lock-up agreement.