SAN FRANCISCO — Facebook declined the most in more than five weeks on concern employees will start selling their shares now that prohibitions on insider sales have ended.

The shares touched $20.73 for the biggest intraday decrease since Sept. 24. They declined 3.8 percent to $21.11 at the close in New York on Wednesday, the first trading session since restrictions on 229 million shares were lifted on Monday. Trading shut down for two days this week because of Hurricane Sandy.