Facebook's share price is getting closer to losing half of its value since its highly anticipated public offering.
It lost 84 cents, or four per cent, to close Thursday at $US20.04.
Another five per cent decline would bring it to $US19 - half of its initial offering price of $US38.
The stock traded as low as $19.82 during Thursday's session.
The share price has been falling since Facebook released quarterly earnings last week for the first time as a public company.
Investors were disappointed despite second-quarter results meeting Wall Street expectations, with revenue one-third higher than last year.
Facebook began trading publicly in mid-May. But since then, investors have been concerned about its ability to keep increasing revenue and make money from its growing mobile audience.
Many analysts hold positive long-term views.