Shares of Facebook are plunging to all-time lows after the expiration of a lock-up period that 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. After one of the most anticipated initial public stock offerings in history, it 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 Thursday, on top of the 421 million already trading.

Facebook Inc. is based in Menlo Park, Calif.