Facebook Inc.’s valuation topped Amazon.com Inc., leaving the social-networking company behind only Google Inc. among U.S. Internet companies.

Facebook is valued at $82.9 billion on secondary exchange SharesPost Inc. and has jumped by more than 40 percent since mid-December. Amazon shares dropped 7.2 percent Friday after a disappointing sales forecast, pushing its stock market value down to $77.2 billion.

Investor demand for Facebook is soaring on the private markets as advertisers pay for the attention of a user base that has ballooned to more than 500 million. Ad spending on Facebook will more than double to $4.05 billion this year, according to researcher EMarketer Inc. LinkedIn Corp., the biggest networking site for professionals, said Jan. 27 that it plans to raise $175 million in an initial share sale.

The gains reflect the rising popularity of social media companies, which let users interact and carry out other tasks that were long unavailable, or only possible to a limited degree, on older Internet sites.

Facebook’s estimated worth surpassed that of eBay Inc., owner of the largest e-commerce market, late last year. It is still dwarfed by Google, the world’s biggest Internet search engine, which is worth $192 billion.

SharesPost, a marketplace for private company shares, bases value on such criteria as transactions, research estimates and venture-funding rounds. Facebook shares have sold for as much as $60 apiece on SharesPost this month, meaning some investors value the social-networking company at $136 billion.

Goldman Sachs Group Inc. led a $1.5 billion financing round in Palo Alto, California-based Facebook at a $50 billion valuation earlier this month.

Facebook plans to start reporting financial results by April 2012 even if it hasn’t held an initial public offering, according to a document sent to prospective investors. The company would be forced to make disclosures because it expects to have at least 500 shareholders by the end of this year, a threshold that makes reporting results necessary under U.S. Securities and Exchange Commission rules, a person who reviewed the document said earlier this month.

At $82.9 billion, Facebook’s value has jumped more than sevenfold since March, when SharesPost introduced its Venture- Backed Index, featuring seven companies. Facebook is over $77 billion more valuable than the second-biggest member, Zynga Game Network Inc., valued at $5.7 billion.

While Facebook’s value is surging on the secondary markets, a poll of global investors showed investor skepticism. Sixty-nine percent of investors in a survey of 1,000 Bloomberg customers, who are investors, traders or analysts, said Facebook is overvalued after the $50 billion valuation implied by Goldman Sachs’s investment.

Amazon, the biggest online retailer, went public almost 14 years ago. The Seattle-based company said Jan. 27 that sales in the first quarter will be as low as $9.1 billion, trailing the average analyst estimate of $9.36 billion in a Bloomberg survey.

Still, Amazon is 17 times the size of Facebook in terms of revenue. With $34.2 billion in sales last year, Amazon trades for 2.2 times revenue. Facebook, said to have 2010 revenue of $2 billion, has a price-to-sales ratio of 41.5.

Amazon fell $13.31 to $171.14 Friday. The shares have gained 36 percent in the past year.

(Bloomberg)