Facebook drops 5% on fourth lockup expiration

• Facebook hit with the fourth unlocking of shares due to lockup expiration
• More than 156 million shares are now able to be sold
• Investors seem increasingly disinterested in Facebook's lockups as time wears on

Facebook stock finished 5% lower Friday as a fourth lockup expired, making more shares available for trading.

The shares closed at $26.81, down $1.43 or 5.06%.

At under $27 a share, the fear is that the sell-off of Facebook (FB) shares could worsen. And despite a rally in recent weeks, the stock remains below its $38 a share IPO price.

The stock is nearly 50% higher than its record low of $17.55. But Friday, 156 million shares of the No. 1 social networking site became available for sale by company insiders and employees.

This is the fourth expiration of IPO-related prohibitions preventing insiders and workers from unloading shares purchased or awarded at or before the IPO on May 18.

The size of the latest unlocking is significant although Facebook has 2.2 billion shares outstanding. Facebook's unlocks have been frequent and unusually large.

As each subsequent lockup has expired, shares have been less affected. Facebook stock fell 6% to an all-time low after the first lockup expired in mid-August. When the second expiration came in late October, the stock fell 3%.

Investors most feared the third and largest lockup expiration, but those concerns turned out to be overdone. On Nov. 14, 777 million shares were unlocked, many of which were owned by company workers. The stock jumped 12% that day, continuing what has become a 50% gain off the stock's record low.

Just one lockup expiration remains, and it's a relatively small one. Roughly 47 million shares held by Mail.ru Ltd. and DST Global investor groups will be available for sale a year after the IPO on May 18, 2013.