UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

(Amendment No. 4)

MILLENNIAL MEDIA, INC.

(Name of Subject Company)

MARS ACQUISITION SUB, INC.

(Offeror)

A WHOLLY OWNED DIRECT SUBSIDIARY OF

AOL INC.

(Parent of Offeror)

(Names of Filing Persons)

Common Stock, $0.001 Par Value

(Title of Class of Securities)

60040N105

(CUSIP Number of Class of Securities)

Julie M. Jacobs

General Counsel

22000 AOL Way

Dulles, VA 20166

(703) 265-1000

(Name, address and telephone number of person authorized to receive notices and communications on behalf of filing persons)

With a copy to:

David E. Shapiro

Wachtell, Lipton, Rosen & Katz

51 West 52nd Street

New York, NY 10019

(212) 403-1000

CALCULATION OF FILING FEE

Check the appropriate boxes below to designate any transactions to which the statement relates:

Check the following box if the filing is a final amendment reporting the results of the tender offer: x

This Amendment No. 4 (this “Amendment”) amends and supplements the Tender Offer Statement on Schedule TO filed by AOL Inc., a Delaware corporation (which we refer to as “Parent”), and Mars Acquisition Sub, Inc., a Delaware corporation (which we refer to as “Purchaser”) and a wholly owned direct subsidiary of Parent, with the Securities and Exchange Commission on September 18, 2015 (together with any subsequent amendments and supplements thereto, the “Schedule TO”). The Schedule TO relates to the tender offer by Purchaser to purchase all of the outstanding shares of common stock, par value $0.001 per share (the “Shares”), of Millennial Media, Inc., a Delaware corporation (which we refer to as “Millennial Media”), at a purchase price of $1.75 per Share, net to the seller in cash, without interest thereon and less any applicable withholding taxes, upon the terms and subject to the conditions set forth in the Offer to Purchase dated September 18, 2015 (the “Offer to Purchase”), a copy of which is attached as Exhibit (a)(1)(A) to the Schedule TO, and in the related letter of transmittal (the “Letter of Transmittal”), a copy of which is attached as Exhibit (a)(1)(B) to the Schedule TO, which together with other related materials, as each may be amended or supplemented from time to time, collectively constitute the “Offer.”

All information contained in the Offer to Purchase and the accompanying Letter of Transmittal, including all schedules thereto, is hereby incorporated herein by reference in response to Items 1 through 9 and Item 11 in the Schedule TO.

This Amendment is being filed to amend and supplement Items 1 through 9 and Item 11 as reflected below and to amend and supplement Item 12 with an additional exhibit.

Items 1 through 9 and Item 11.

Items 1 through 9 and Item 11 of the Schedule TO are hereby amended and supplemented as follows:

“The Offer and withdrawal rights expired as scheduled at 11:59 p.m. (New York City time), on October 22, 2015 (such date and time, the “Expiration Time”), and the Offer was not extended. Purchaser was advised by the Depositary that, as of the Expiration Time, a total of 114,871,644 Shares had been validly tendered into and not withdrawn from the Offer, representing approximately 80.3% of the aggregate number of Shares then issued and outstanding. In addition, Purchaser was advised by the Depositary that, as of the Expiration Time, Notices of Guaranteed Delivery had been delivered with respect to 1,283,015 Shares, representing approximately 0.9% of the aggregate number of Shares then issued and outstanding. Accordingly, the number of Shares tendered pursuant to the Offer satisfied the Minimum Condition.

All conditions to the Offer having been satisfied, Purchaser accepted for payment, and has paid for by deposit of the Offer Price for such Shares with the Depositary, all Shares validly tendered into and not validly withdrawn from the Offer.

As a result of its acceptance of the Shares tendered in the Offer, Purchaser acquired sufficient Shares to consummate, and on October 23, 2015 did consummate, the Merger without the affirmative vote of the stockholders of the Company pursuant to Section 251(h) of the DGCL. At the Effective Time, each of the then issued and outstanding Shares (other than Shares held (i) in the treasury of Millennial Media or by Parent or Purchaser, which Shares were canceled and ceased to exist, (ii) by a wholly owned subsidiary of Millennial Media or Parent (other than Purchaser) or a wholly owned subsidiary of Purchaser, which Shares were converted into shares of the Surviving Corporation representing the same percentage ownership in the Surviving Corporation that such holder owned in Millennial Media prior to the Effective Time and (iii) by stockholders who validly exercised appraisal rights under Delaware law with respect to such Shares) were automatically cancelled and converted into the right to receive cash in an amount equal to the Offer Price, without interest thereon and subject to any required tax withholding.

All Shares will be delisted from and will cease to trade on the New York Stock Exchange, and the Company will be deregistered under the Exchange Act.

On October 23, 2015, Parent issued a press release announcing the expiration and results of the Offer and the completion of the Merger. The full text of the press release is attached as Exhibit (a)(5)(H) to the Schedule TO and is incorporated herein by reference.”

Exhibits.

Item 12.

Item 12 of the Schedule TO is hereby amended and supplemented by adding the following exhibit:

SIGNATURES

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

EXHIBIT INDEX