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Facebook director Andreessen's firm sells a third of its shares

Marc Andreessen, co-founder and partner of Andreessen Horowitz, speaks during the panel discussion "In Tech We Trust? A Debate with Peter Thiel and Marc Andreessen" at the Milken Institute Global Conference in Beverly Hills, California April 29, 2013. REUTERS/Fred Prouser

NEW YORK (Reuters) - Facebook Inc director Marc Andreessen's venture-capital firm sold a third of its stake in the world's No. 1 online social network, according to a recent regulatory filing.

Andreessen Horowitz sold 2.28 million shares on November 6 at about $49 to $50 a share, according to a filing with the U.S. Securities and Exchange Commission on Friday. It still holds 4.57 million shares in Facebook.

Andreessen Horowitz spokeswoman Margit Wennmachers said on Sunday that the firm's investment thesis was successful. Still, she said they are big believers in Facebook, which is why they are holding on to big portion of their shares.

Facebook shares closed at $47.53, down 3 cents on Friday.

Marc Andreessen helped start browser company Netscape, which was acquired by AOL Inc in 1999. Andreessen Horowitz has invested in some of the country's hottest start-ups, including Facebook and online bulletin board Pinterest.

(Reporting By Dhanya Skariachan and Alexei Oreskovic, writing by Michael Erman; Editing by Diane Craft)