Reid Hoffman, chairman and co-founder of LinkedIn Corp., third from left, and Jeffrey Weiner, chief executive officer of LinkedIn, center, applaud during the opening bell ceremony at the New York Stock Exchange. (Michael Nagle/BLOOMBERG)

Call it the viral IPO.

The social-networking company Linked­In debuted on the New York Stock Exchange on Thursday to a thunderous welcome that harkened back to the frenetic days of the dot-com bubble. Its stock price skyrocketed nearly 100 percent just minutes after trading began — a level virtually unseen in the past decade — and turned its executives into billionaires.

The company’s meteoric rise is seeding fears of a second Internet bubble. But this one, analysts say, is not driven by Wall Street alone.

LinkedIn made Twitter’s list of trending topics Thursday and was the second-most-searched term on Google, falling behind only “end of the world may 21st.” It was mentioned in 1,142 Facebook posts, 2,569 blogs and more than 34,000 tweets, according to the analytics firm Webtrends, as LinkedIn rode the same wave of social media that it helped create.

“The social network priced this deal,” said Kathleen Shelton Smith, principal at Renaissance Capital, an IPO investment advisory company that had record traffic to its Web site Thursday. “Sometimes these feed on themselves.”

The reception seemed to catch even LinkedIn executives off guard. The company — which has said it does not expect to make a profit this year after earning $15 million in 2010 — announced its plans to go public in January. It announced the initial share price this month at $32 to $35 and then upped the offer to $45 this week. On the private stock exchange SharesPost, investors had valued LinkedIn at $2.5 billion.

Wall Street blew past those expectations Thursday, starting the stock at $83 and bidding as high as $122.70. It closed at $94.25 — up 110 percent for the day — with a value of nearly $9 billion. That prompted some analysts to question whether LinkedIn should have asked for more.

“We are very comfortable with where we priced,” LinkedIn chief executive Jeff Weiner said in an interview on Bloomberg TV. “I wouldn’t read too much into any one day of trading.”

But for many investors, Linked­In’s debut is just the appetizer before a bigger fish: Facebook. The company is expected to go public next year, and secondary markets have valued it at more than $75 billion, though predictions have moderated in recent months to $55 billion.

Investors are also looking to LinkedIn for a sign that the IPO market — which dried up during the recession — is back in business. That could set the stage for other popular sites such as Group­on to go public.

“People have this pent-up demand to invest in the space,” said Ray Valdes, an analyst at Gartner Research. “They’re getting some of that investor love, whether they deserve all of it or not.”

Some of that sentiment was playing out online as well. “Wow! LNKD is partying like it’s 1999,” tweeted one user, referring to the company’s ticker symbol.

LinkedIn reported total revenue of $243 million last year, earning about 7 cents per share. That means it traded for more than 1,300 times revenue on Thursday. The company said it plans to use the cash to purchase smaller companies, invest in its network and expand its international operations.

In addition, though LinkedIn is most widely known for its social network, the company gets half its revenue by helping businesses find and recruit employees. Thirty percent of sales comes from marketing, and only 20 percent of revenue stems from users. The model distinguishes itself from other social-networking sites that rely heavily on ads.

“It’s not like this is a,” said Lise Buyer, founding principal of IPO consulting company Class V Group. “Clearly it is a terrific, legitimate company they have.”

Whether investors’ enthusiasm reaches bubble status will depend on the circumference of LinkedIn’s halo effect. Buyer noted that investors were salivating for shares of Renren, the Chinese version of Facebook, when it went public two weeks ago. The stock climbed 29 percent on its first day, to $18.01. By Thursday, it had fallen nearly 24 percent, to $13.75.

“The first day is really interesting,” she said. But “what really matters is ever afterwards.”