Facebook closed out its first full week of trade with a loss of 16% from its offering price of $38, in a huge disappointment after a much-hyped initial public offering worth $16-billion, the biggest for a tech firm. The stock failed to live up to the anticipation of some who thought investors would be stampeding to get a piece of the network, which has 900million users.

"When you see Facebook share prices tank, it does get people back on to a more foundational basis, in terms of real revenues, real profits," said Nick Landell-Mills at Indigo Equity Research.

Mark Heesen, president of the National Venture Capital Association, said investors are being more cautious than during the tech bubble of the late 1990s.

"This is by no means the end of social media. It is going to continue to grow and expand," he said.

But he said that during the tech bubble, "venture capitalists invested $150-billion in two years. In the last two years we invested about $60-billion. There is much, much less money in the system right now. That's critically important."

Gerard Hoberg, professor of finance at the University of Maryland, said he does not expect a new bubble. "I think it's very healthy and I think people learned the lessons from the 1990s," he said. "It's preventing a bubble from forming." Facebook appeared to be the driving force in a surge into social media. But some of its social media brethren are also being watched cautiously.

Zynga, the social gaming website that has strong ties with Facebook, has lost 35%, and online deals firm Groupon has slid nearly 40%. But professional social network LinkedIn has doubled in a year since its IPO. Heesen said the mixed reaction to these IPOs has taken some of the froth out of the market.