SAN FRANCISCO » This much is very clear: There’s a lot of interest in Pinterest, one of the high-fliers of this Internet boom.

The popular social networking site is in talks to raise more money at a blockbuster $2-billion to $2.5-billion valuation. That’s according to the Wall Street Journal, which said the deal has not been finalized. A Pinterest spokeswoman declined to comment.

Pinterest is one of a growing number of billion-dollar Bay Area start-ups. It raised $100 million in May in a deal that valued the San Francisco company at $1.5 billion. Since then apparently other investors have decided they’d like to try a "Pin It" button, too.

Facebook’s rocky reception on Wall Street has not cooled demand from investors for social media starlets. Valuations for many Internet companies have declined as a result of Facebook’s initial public stock offering. But the brightest prospects are still seeing their valuations soar into the stratosphere.

"Only a relative handful of companies are getting these high valuations," University of Florida professor of finance Jay Ritter said. "It’s a winner-take-all environment. If you’ve got the platform or the technology that everyone wants to use, you have won the market. And the winning companies get the spoils of victory."

Many of these companies are scoring high valuations even though they have yet to build businesses or generate revenues. So investors are gambling on "potential value," Ritter said.

IPODesktop.com’s Francis Gaskins says investors are placing too much stock in that potential. He called the rumored Pinterest valuation a “stretch.”

"There seems to be a valuation bubble for private tech companies in Silicon Valley," Gaskins said. "I think a lot of it is based on the expectation of growing into their billion-plus valuations. It’s not clear that Pinterest has much actual revenue now, and ultimately in the IPO market it does come down to top-line revenue growth and how soon to break even."

Lise Buyer, principal at Class V Group, an IPO advisory firm, said the valuation — if in fact true — would have taken several factors into account.

"The market is always full of highly inaccurate hype, so until it’s done and announced, it’s just a rumor," Buyer said. "If the number is correct, one could assume the valuation reflects a combination of factors including the company’s undeniable success to date, presumably some solid conversations about a long-term, sustainable business model, and of course the number of investors that would like to participate in the enormous marketplace Pinterest has unearthed and fostered."

Social media investor Lou Kerner says Pinterest has earned the valuation. Pinterest’s monthly unique user visits shot up to more than 28 million in December, up from 7.5 million a year earlier, according to research firm ComScore.

"Pinterest is rapidly emerging as another major social network, their niche being sharing ‘what I like,’" Kerner said. "Pinterest usage and engagement continue to grow at impressive rates. We’ve seen the other major social networks (Facebook and Twitter), both further along than Pinterest, grow to valuations of $68 billion and $9 billion, respectively. So at $2 billion or $2.5 billion, there is still lots of upside for investors."