Facebook's stock is getting closer to losing half of its value since its highly anticipated public offering.

It lost 84 cents, or 4 percent, to close Thursday at $20.04. Another 5 percent decline would bring it to $19 - half of its initial offering price of $38. The stock traded as low as $19.82 during Thursday's session.

The stock 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.