"At $100 a share, we would not be buyers," Veru said. "It far exceeded our expectations for what it would do in the first day of trading. It would be amazing to me, with the revenue base it has, if it maintains a $10 billion market cap."

LinkedIn's performance yesterday is reminiscent of some of hottest stocks in the dot-com boom. Yahoo! Inc. rose 154 percent on its first trading day in 1996, a year after Netscape Communications Corp. more than doubled in its debut.

More recently, Google Inc. rose 18 percent in its 2004 IPO, and VMware Inc. surged 76 percent when it started trading in 2007.

"The valuation for LinkedIn is rich," said Michael Moe, chief investment officer of GSV Capital Management in Woodside, California, in a televised interview with "Bloomberg West." "To earn the valuation, it has to continue to grow very, very fast."

Qihoo 360 Technology Co., the Beijing-based provider of computer anti-virus products and Web browsers, had the biggest first-day gain among U.S. IPOs this year, surging 134 percent after raising $175.6 million in its offering.

Backers Gain

LinkedIn's backers, which have made more than $100 million in investments in Mountain View, California-based LinkedIn since 2003, stand to gain. Sequoia Capital has amassed a holding now worth $1.59 billion, and Greylock Partners has a $1.32 billion stake, based on yesterday's close. Reid Hoffman, LinkedIn's founder and chairman and its biggest shareholder, holds $1.8 billion and Bessemer Venture Partners has a stake worth $431.5 million.

Members of LinkedIn use the site to search for jobs, recruit employees and find industry experts. While users can create personal profiles for free, paid subscriptions were introduced in 2005, giving recruiters more access to candidates and providing professionals ways to communicate with one another.

While LinkedIn is often compared to social networks such as Facebook and Twitter Inc., which depend on advertising to consumers, the company said in its prospectus that a "substantial portion" of revenue comes from a business that's comparable to the software-as-a-service model. That's where companies deliver software over the Internet, a market expected to climb 16 percent this year to $10.7 billion, according to Gartner Inc., a research firm in Stamford, Connecticut.

Business Software

SaaS companies, including Salesforce.com Inc., NetSuite Inc. and SuccessFactors Inc., sell subscriptions over the Internet rather than long-term licenses like traditional business-software companies.