It hit that milestone on Friday, a day after the expiration of a lock-up period. The lock-up's end has provided some early investors and insiders with an opportunity to sell shares.
Investors have been concerned about Facebook's ability to increase revenue and make money from its growing mobile audience. Many analysts, however, hold positive opinions of the company's long-term prospects.
The stock closed on its first day barely above its initial public offering price of $38. It has been below that level since.
On Friday, the stock fell 87 cents, or 4 percent, to $19 in afternoon trading.
(Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)
8/17/2012 1:21:09 PM (GMT -7:00)