Shares in Facebook dropped 4.1 percent

Shares in Facebook, the world's largest social-networking service, dropped 4.1 percent to $19.05 at the close in New York. Facebook earlier fell to as low as $19, after the number of shares available for trading increased 60 percent yesterday.

The decline reflects concern that more sales will follow in the coming months as additional lock-ups expire and as the company struggles to wring sales from a growing customer base, said Rory Maher, an analyst at Capstone Investments Inc.

The 6.3 percent drop in Facebook shares yesterday was the second-largest post-lock-up decline among companies that have gone public since January 2011.