A US probe into Goldman Sachs’s massive investment in Facebook could drive the hugely popular social-networking website to go public earlier than it hoped for, analysts said.

The investment, reported at $450 million, has exposed the thin line between private and public markets and underscored companies’ reluctance to launch an initial public offering (IPO) of shares that results in oversight by regulators.

“Companies are doing everything they can do to avoid going public. Facebook is a prime example,” said James Angel of the McDonough School of Business at Georgetown University.

“We’ve made it much more difficult in the United States to be a public company. We’ve made it much more expensive, the legal risks and the trading environment have also changed.”

US media said that Goldman invested $450 million, together with Russian investment firm Digital Sky Technologies (DST) which sank another $50 million into the social-networking site.

The $500 million deal values Facebook at a whopping $50 billion, more than longstanding giants such as Boeing, Time Warner and Yahoo!

The Goldman-DST deal allows Facebook to tap capital markets, while avoiding some of the constraints of trading publicly.

“The big incentive to be a public company is that it is easier to have a trading market for your shares, but if there is a shadow market that provides as much liquidity as the public trading market than companies will not be interested in going public,” said Adam Pritchard of the University of Michigan Law School.

“Some people might (ask) ‘why should only Goldman’s favored friends get the chance to invest in Facebook?’” said Mr Angel.

There are also concerns the investment could create a shadow exchange market beyond the scrutiny of regulators, exposing investors to potential risks due to the lack of transparency rules.

Facebook reportedly netted $200 million in profit in 2010, and analysts have said its revenues in 2011 could be as high as $2 billion.