Ownership Submission
FORM 3
 UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  COSTAR GROUP INC
 2. Date of Event Requiring Statement (Month/Day/Year)
04/27/2011		 3. Issuer Name and Ticker or Trading Symbol
LoopNet, Inc. [LOOP]
(Last)
(First)
(Middle)
1331 L STREET, NW		 4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
_____ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

WASHINGTON, DC 20005		 6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)		 2. Amount of Securities Beneficially Owned
(Instr. 4)		 3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)		 4. Nature of Indirect Beneficial Ownership
(Instr. 5)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
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Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)		 2. Date Exercisable and Expiration Date
(Month/Day/Year)		 3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)		 4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)		 6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
COSTAR GROUP INC
1331 L STREET, NW
WASHINGTON, DC 20005		     X    

Signatures

/s/ Brian J. Radecki, Chief Financial Officer 05/06/2011
**Signature of Reporting Person Date

Explanation of Responses:

No securities are beneficially owned

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
 
Remarks:
(1) CoStar Group, Inc. (the "Reporting Person") is filing this statement solely because, as a result of a Voting and Support Agreement, dated as of April 27, 2011 (the "Voting Agreement") among the Reporting Person, LoopNet, Inc. ("LoopNet"), and the holders of LoopNet's Series A Convertible Preferred Stock and certain of LoopNet's executive officers and members of LoopNet's board of directors (collectively, the "Stockholders"), the Reporting Person may be deemed to have beneficial ownership of shares of common stock, par value $0.001 per share, of LoopNet ("Common Stock") beneficially owned by the Stockholders. The Voting Agreement was entered into in connection with the Agreement and Plan of Merger (the "Merger Agreement"), dated as of April 27, 2011, among the Reporting Person, LoopNet and Lonestar Acquisition Sub, Inc.

(2) Neither the filing of this statement nor any of its contents shall be deemed to constitute an admission by the Reporting Person that it is the beneficial owner of any Common Stock referred to herein for purposes of Section 16 of the Securities and Exchange Act of 1934, as amended (the "Act"). The Reporting Person has no pecuniary interest in such Common Stock. The Reporting Person, pursuant to Rule 16a-1(a)(4) promulgated under the Act, hereby expressly disclaims that it is the beneficial owner of such Common Stock.

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