Online discount start up site Groupon that recently rebuffed a $6-billion takeover from internet giant Google, has raised $500 million in its latest round of funding that is more than halfway towards its goal of raising $950 million. 

The three-year-old Chicago-based Groupon revealed the fund raising in a filing with the US Securities and Exchange Commission. The company has also disclosed in its filing that it still plans to raise upwards of another $450 million, to bring the total amount of financing to $950 million.

The latest fund raising gives Groupon a valuation of $4.75 billion.

Although the company has not revealed its new investors, various media reports indicate that its new backers could include Morgan Stanley, T Rowe Price and Fidelity Investments, while it's previous investor Russia's Mail.ru Group, formerly Digital Sky Technologies, could also have invested in this round.

Groupon recently offered to buy back 15 per cent of its stock from current shareholders, and the SEC filing indicates that the company intends to use $345 million of the $500 million raised to buy out stock from investors and management.

Groupon, the brainchild of its current CEO Andrew Mason, was launched in 2008 and is an electronic commerce site that has its spread in more than 300 markets and 35 countries having more than 33 million subscribers, making it one of the fastest-growing companies in history. 

Groupon operates a shopping website that offers a daily deal on local goods, services, and cultural events for businesses and consumers in the US. It provides daily deals on acupuncture, meals, opera tickets, tours, teeth cleanings, restaurants, theatres, spas, classes, sporting events, bars, museums, concerts, and gyms.

Though the company has never disclosed its revenues, analysts estimate its annual revenue ranging from $500 million to $2 billion.

Its main investors include private equity firms Accel Partners, New Enterprise Associates and Battery Ventures and Mail.ru Group, which has also invested in social networking site Facebook.