Facebook Inc.'s 6.3 percent drop yesterday, after the end of restrictions on share sales by its biggest investors, was the second-largest post-lock-up decline among companies that have gone public since January 2011.

Only social-game maker Zynga Inc. tumbled more, losing 7.9 percent, on the first day that insiders could start selling their stakes, data compiled by Bloomberg show. That was the largest one-day post-lock-up descent among the 20 biggest initial public offerings since January 1, 2011. The slump yesterday left Menlo Park, California-based Facebook at a record low after a 60 percent increase in the number of shares available for trading.

Under restrictions worked out with IPO underwriters, early investors agree not to sell their holdings for a preset period after a market debut to keep from flooding the market with shares. Facebook's 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.