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.
The lockup was designed to prevent a flood of shares hitting the market immediately after the company’s initial public offering in May. Current and former Facebook employees have seen the value of their equity compensation decline; the stock fell 42 percent through Monday. Some employees are eager to realize gains, said Michael Pachter, a Wedbush Securities analyst.
‘‘The bulk of their compensation is stock, and probably a whole lot of them are living way above what their salary will justify,’’ Pachter said.
Shares of Facebook made available for trading are held by current and former employees, according to a regulatory filing. The lockup will expire for an additional 960 million shares by the end of the year, followed by 47.3 million more in May 2013.
Chief executive Mark Zuckerberg’s cache of 444 million shares and options for 60 million more is excluded from the tally because he has said he won’t sell before September 2013, according to the filing.
The first lockup on Facebook stock expired Aug. 16, freeing 271.1 million shares held by early investors including Goldman Sachs and Accel Partners.
Facebook reported last week that third-quarter sales rose 32 percent, beating analysts’ predictions, as the company began to benefit from efforts to sell adds targeted at the growing number of users who access the service via mobile devices. The growth matched the second quarter’s pace, snapping a streak of slowing increases.
The company’s market value has plummeted since it held the largest Internet IPO on record.
Facebook’s mobile growth prospects are promising as users show more engagement on wireless devices than on desktop computers, Zuckerberg said on an earnings-related call. The company may eventually make money more easily from mobile ads than those on desktops, he said.
About 60 percent of Facebook’s more than 1 billion members are accessing the service on mobile, compared with about 47 percent a year earlier.