A NEW LOW: Facebook's stock plunged to a new low Thursday as some of the social networking leader's early backers got their first chance to sell shares since the company's rocky initial public offering.

WHY? Investors who owned a combined 271 million Facebook shares could have sold their holdings with the expiration of a ban known as a lock-up period. There are more expiration dates coming in the fall and as late as next May.

HIGH VOLUME: More than 156 million shares were traded, more than five times the stock's average volume over the past month. Analysts interpreted the high volume as a sign that at least some of the insiders were selling.