Shares of the online professional social networking company soared 171 percent, or $76.97, to $121.97 in afternoon trading on the New York Stock Exchange — far exceeding the $45 initial public offering price.

The stampede brings the valuation of LinkedIn, which less than a decade ago was no more than an ambitious idea and a computer in one man’s living room, to more than $11 billion. Just two weeks ago, LinkedIn proposed a price range for the IPO that valued it at just over $3 billion.

LinkedIn is the first prominent US social networking company to publicly test just how hungry investors are for anything social-media related on the Web such as Facebook, Groupon, Twitter and Zynga.

Such exuberant debut trading in recent years has been the prerogative of Chinese Internet stocks, unmatched by their US peers.

LinkedIn is the first US Web company to replicate the jump, marking the biggest first-day price jump since shares of Baidu, a Chinese Internet search engine, rose 354 percent in their Nasdaq debut in 2005.

LinkedIn Chief Executive Jeff Weiner — a newly minted millionaire — shrugged off the trading craze or even worries that the pricing underestimated the appetite for the stock.

“Speaking for myself, personally I’m not even thinking twice about where the price is today and leaving money on the table or even anything remotely along those lines,” he said, adding that the stock “will take care of itself” and trade on fundamentals.

He also cautioned against viewing LinkedIn as a proxy for other big-name IPOs potentially coming to the markets, saying they will also be driven by those companies’ fundamental values — which are, in turn, far from echoes of the dot-com bubble.

Weiner, who sold about 5 percent of his holdings in the offering, made $5.2 million on the IPO based on the latest stock price, while his remaining stake in LinkedIn is worth almost $270 million.

LinkedIn’s co-founder and ex-PayPal executive Reid Hoffman made $5.2 million selling less than 1 percent of his shares. His remaining stake in the company — 21.7 percent of the voting power — is now worth about $2.3 billion.

Mountain View, California-based LinkedIn raised $352.8 million on Wednesday by selling about 8 percent of the company, or 7.84 million shares, for $45 apiece. The company increased its anticipated price range by $10 on Tuesday to $42 to $45 per share.

From the midpoint of the original price range to the current price, shares have more than tripled.

“The public market demand turns out to be even stronger substantially stronger than private market transactions have been implying,” said Jay Ritter, IPO expert and professor of finance at University of Florida. He added private-market trading of LinkedIn shares in the runup to the IPO gave the company a valuation of about $3 billion.

“This has certainly been a bullish event for the valuations of Twitter and Facebook and other similar companies,” he said.

The company’s shares were sold at about 17.5 times its 2010 sales. By comparison, Google Inc’s shares are valued at about six times 2010 sales.

Renren shares gained 4.5 percent to $14.32 while MySpace parent News Corp rose 1.1 percent to $17.71. Google, owner of YouTube, was little changed.

Underwriters on the IPO were led by Morgan Stanley, Bank of America Merrill Lynch and JPMorgan.