NEW YORK (AP) - Shares of Facebook are plunging to all-time lows after the expiration of a lock-up period which has provided early investors and insiders with an opportunity to exit.

The stock fell 7 percent, or $1.49, to $19.71 in Thursday morning trading.

If the stock hits $19, it will have lost half its value since Facebook went public in May.

It's been a rough run for Facebook which, after one of the most anticipated initial public stock offerings in history, suffered what may be the most botched IPO as trading glitches marred its first day. It's been almost all downhill since then.

In all, 271 million shares will become eligible for sale this week, according to Facebook's regulatory filings. That's two-thirds of all shares.

Facebook Inc. is based in Menlo Park, Calif.