With Facebook, it’s not a question of if it files for an IPO, its a matter of when. Whilst rumours have been circulating since the middle of last year, a new report from AllThingsD suggests the social networking giant is aiming to go public in the third week of May.

The technology publication cites multiple sources, suggesting that if the goal is to hit its target of a late May IPO, Faceboook will submit its S-1 filing within the next month, taking into account that the “Securities and Exchange Commission usually takes about three to four months”.

In June 2011, we reported that Facebook was aiming to file an S-1 towards the end of the year, looking to IPO in 2012. CNBC noted that the social network would look at a valuation that exceeded $100 billion. At the time, Facebook had been trading on the secondary market with a valuation of around $85 billion, with some share prices pushing the $100 million price point.

Facebook’s COO Sheryl Sandberg stated a few weeks previous to the report that the company’s IPO was “inevitable” and said that it was “a process that all companies go through”.

Facebook is expected to hit 1 billion users by the Summer, increasing its reported $4 billion revenue in 2011 by a third in 2012. The company’s impending IPO is likely to spark the next crop of angel investors, becoming one of the biggest Web offerings ever.