Facebook shares hit a new all-time low Thursday after early investors got their first chance to sell, dropping the stock price below the $20 mark and extending the losses its seen since the company’s $38 debut on May 18.

The drop makes Facebook the second-worst post-lockup performer among companies that have gone public since January 2011, Bloomberg reported. The worst performer? Facebook buddy and social gaming giant Zynga.

The declines could speak to skittishness about digital goods. And, in Facebook’s case, there’s additional concern that the company won’t be able to mon­etize the habits and information of its over 900 million users.

The social network has been quiet about its stock performance in public statements. But, according to a report from The Wall Street Journal, Facebook chief executive Mark Zuckerberg acknowledged employee anxiety over the stock’s performance during meetings within the company.

In a meeting earlier this month, Zuckerberg said the stock’s performance may be “painful” for investors to watch, unnamed sources told the WSJ, but added that he believes the company’s plans and investments will pay off in the long term. That’s also the general feeling of analysts such as Arvind Bhatia of Sterne Agee, who said in a recent note that he expects the company to improve its performance in the second half of the year.

There could be more pain in the cards for Facebook, however, as more stock lockups are set to expire before the end of the year. Employees who’ve received Facebook shares as compensation will become eligible to sell their shares by the end of the year. The Wall Street Journal reports that the number of shares still poised to hit the market exceeds 2 billion. Expirations in October, November and December will release 1.4 billion shares, and the last release will come next May.

The stock was trading around $20.00 at the market’s open on Friday.

(Post Co. Chairman and Chief Executive Donald E. Graham is a member of Facebook’s board of directors.)

Related stories:

Facebook stock hits new low after freeing new shares

A Facebook court battle: Is ‘liking’ something protected free speech?

FTC finalizes Facebook settlement