The stock fell 50 cents, or 1.9 percent, to close Thursday at $26.31. It's down 31 percent from its initial public offering price of $38.
Facebook's stock began trading publicly on May 18. Investors are concerned about its ability to keep increasing revenue and make money from its growing mobile audience, though many analysts hold positive long-term opinions.
The decline comes the day after the Nasdaq stock exchange announced it will give out $40 million in cash and credit to reimburse investment firms that lost money on Facebook's opening day. That first day began with computer glitches at the exchange.
Facebook Inc., based in Menlo Park, Calif., has nearly a billion users.
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