NEW YORK - LinkedIn's stock nearly doubled in its market debut because of huge investor demand for the first major U.S. social networking company to go public.

The stock traded at $87.11, up 94 percent, Thursday morning after debuting at $83 and briefly reaching $92.99.

Trading in the stock didn't begin until almost 10 this morning, not unusual in a hotly anticipated IPO.

Renaissance Capital, an IPO research and investment firm, said LinkedIn's 84 percent increase at the open was the biggest for a U.S. IPO since the 2009 debut of OpenTable Inc., a restaurant reservations website.

IPO analyst Scott Sweet, the founder of IPO Boutique, credits the increase to LinkedIn selling a relatively small number of shares, 7.8 million. Main Street investors clamored for the job networking site's shares, which had only been available to the country's biggest mutual funds, pension funds and other major institutional investors in an initial public offering Wednesday evening.

LinkedIn Corp.'s IPO had been priced at $45 per share, at the high end of the company's initial target. The company had raised $353 million Wednesday night in an IPO that valued it at $4.3 billion. That's the largest valuation for a U.S. Internet company since Google went public in 2004.

The company's service helps businesses find new employees and promotes networking among the more than 102 million people that have set up profiles.

Sweet said the "monstrous interest" in LinkedIn and its sharp climb Thursday were good signs for other social networking companies such as online messaging service Twitter, Web game maker Zynga, coupon site Groupon and Facebook.

LinkedIn is trading under the symbol "LNKD" on the New York Stock Exchange.

Most analysts believed that demand would send shares higher in their first day of trading even though the IPO price already was well above LinkedIn's initial target of $32 to $35 per share.

The lofty $4.3 billion appraisal of LinkedIn reflected investors' belief that Internet services that connect people with common interests would be able to make more money as the Web's audience steadily expands.

LinkedIn's valuation eventually may look modest compared with that of other Internet companies that are being touted as potentially going public in the next 18 months. The short list includes online messaging service Twitter, Web game maker Zynga, coupon site Groupon, and Facebook, the social network that boasts more than 500 million users.

LinkedIn, based down the street from Google's Mountain View, Calif., headquarters, runs a website that serves as part-Rolodex, part-hiring center for workers trying to meet people who might further their careers and businesses searching for talented employees. More than 102 million people have set up LinkedIn profiles so far. Another million join each week.

The company makes most of its money from fees charged for better access to the data on its website. It earned $3.4 million on revenue of $243 million last year, but expects to lose money this year as it invests in new products and more computers to run its services.