Shares in Facebook have fallen for the second straight day, causing analysts to intensify their criticism of how last Friday's Initial Public Offering (IPO) was handled.

After requiring intervention from underwriters to stay in the black on day one of trading, days two and three have both seen drops, to US$34.03 at close of trading on Monday and now to US$31, an 18.4% drop from the opening price of US$38.

It's the actions of underwriters just before IPO that's really causing concern, though, with the Wall Street Journal reporting that both Morgan Stanley and Goldman Sachs revised their financial forecasts for the stock during the IPO roadshow, but only told some of their investors.

In a scathing blog post, financial analyst Barry Ritholtz states that he can't recall that ever occurring during an IPO roadshow.

"I would not be surprised to see [Facebook stock] eventually cut in half from the way-too-high offering price,” Ritholtz says.

The operators of the Nasdaq exchange have also copped criticism for the technical glitch that delayed the start of trading on Friday.

Securities and Exchange Commission chairman Mary Schapiro has even launched an investigation into the IPO ‘in an effort to ensure confidence in public markets'.

Facebook wasn't helped by major advertiser General Motors pulling its Facebook advertising just days before the IPO, casting doubts on the growth potential of Facebook's advertising revenue.