The social network shares turn green on their fourth day of trading - but there's more bad news on the regulatory and legal front.

Facebook’s stock is being restructured into a two-tier system of Class A and Class B shares.

The social networking site’s current owners are set to convert their stock into Class B shares, which have 10 times the voting power - allowing them to maintain control even if public float leaves them with a minority holding.

The restructure - first reported by The Wall Street Journal - is widely seen as the precursor to an IPO.

Signs point to the social networking site preparing for an IPO. Its current CFO is out, and Facebook is looking for a replacement “with public company experience.”

In October 2007, Microsoft invested $US240 million for a 1.6% stake in Facebook, implying the privately held company had a value around $US15 billion.

But recent private equity trades executed by founder Mark Zuckerberg indicate Facebook’s value has plunged by around 90%.