Shares of Facebook (Nasdaq: FB), the No. 1 social network, plunged as much as 4 percent in early Friday trading, reversing Thursday's 5 percent gains.

In the first 30 minutes of trading, Facebook fell to $28.46 down $1.14  after dropping as low as $28.40. The fall came despite a new outperform recommendation from Robert W. Baird, with a price target of $37.

As well, Pivotal Research upgraded shares of the Menlo Park, Calif., company from sell to hold in light of its plunge from its initial public offering price of $38.

Ford Motor Co. (NYSE:F), the No. 2 U.S. car maker, said it would expand its ads on Facebook. Two weeks ago, General Motors Corp. (NYSE: GM), the No. 1 maker, withdrew its $10 million account on grounds Facebook's platform hadn't been effective.

Two weeks after the May 18 IPO, 24 firms have made recommendations on Facebook, Reuters estimate show. The average price target is $40. For the second quarter ending June 30, analysts expect net income of $324 million, or 15 cents a share, on revenue of $1.17 billion.