Facebook Inc director Marc Andreessens venture-capital firm sold a third of its stake in the worlds 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 firms investment thesis was successful.