SAN FRANCISCO (REUTERS) - Pinterest has won a US$225 million (S$279 million) round of equity funding that values the virtual scrapbooking company at US$3.8 billion, two people with knowledge of the investment said on Wednesday.

The deal, led by Fidelity Investments, makes Pinterest one of the most valuable privately held consumer Internet companies just 2 1/2 years after it secured its first round of venture capital financing in May of 2011.

The funding was first reported by AllThingsD.

Fidelity will not take a board seat as part of the deal, the person said. Previous venture capital investors, including Bessemer Venture Partners, Firstmark Capital, Valiant Capital Management and Andreessen Horowitz, also participated in the latest round.

In just the past 18 months, Pinterest's valuation - it was pegged at US$1.5 billion last May - has ballooned in dramatic fashion without proof of its money-making ability.

Chief executive Ben Silbermann unveiled a revenue strategy last month when he announced a "promoted pins" advertising product.

Still, with Twitter Inc IPO-TWTR.N primed to go public in a matter of weeks, the spotlight could shift to Pinterest as a hot social media prospect coming down the IPO pipeline.

Like Twitter, Pinterest is among the most popular of the fast-growing crop of social media websites, but there remain signs that the company is struggling to keep many of its users coming back.

According to a recent survey by Reuters and Ipsos, 26 per cent of the 807 people polled that had signed up for Pinterest said they do not use the service anymore and 9 per cent of people who signed up have since shut down their accounts. The results have a credibility interval, a measure of accuracy, of plus or minus 3.9 per cent.

Pinterest did not immediately respond to a request for comment.