Groupon filed for its initial public offering Thursday after weeks of speculation that the company was ready to go public.

In its filing with the Securities and Exchange Commission, the daily deals site reported selling 28.1 million Groupons in the first quarter of 2011.­­

Groupon revealed that has increased its revenue from $3.3 million in the second quarter of 2009 to $644.7 million in the first quarter of 2011. But it’s still not a profitable business, having lost $146.5 million in its first quarter.

The deal is being underwritten by Morgan Stanley, Goldman Sachs and Credit Suisse. The company’s proposed stock ticker symbol is GRPN. The company expects to raise as much as $750 million from its IPO.

Many will be watching Groupon closely after social network LinkedIn’s huge first day of trading, which raised the company’s value to nearly $9 billion. Game company Zynga and Facebook are expected to file for their IPOs in the next two years.

Shares of LinkedIn climbed as high as $122 after its initial public offering, prompting some to say that the tech industry is on the verge of a new tech bubble. Linkedin shares are currently priced at around $80 per share.

Related stories:

LinkedIn IPO shatters expectations

LinkedIn IPO hits $9 billion -- a new tech bubble?

LinkedIn raises IPO — and eyebrows