According to a report by comScore Inc, Facebook has accounted for about 28 percent of online display-advertisements in 2011.

The social networking giant had recorded 21 percent of impressions in the previous year, according to comScore. Facebook remained ahead of Yahoo, which remained No. 2 with 11 percent while Microsoft was third at 4.5 percent.

Facebook is planning to open its initial public offering soon. Facebook might come out with its long-anticipated initial public offering (IPO) in the third week of May 2012. The event will gather much interest in the Silicon Valley this year as Facebook joints many young firms in going public. All Things Digital blog of The Wall Street Journal reported this Monday that Facebook's IPO is expected in the third week of May.

Facebook's share of the U. S. online display advertising market grew to about 28% for 2011 up from 21 per cent in the previous year. Facebook had surpassed Yahoo for the first time in 2009, according to ComScore's vice president of marketing and industry analysis.

Lipsman said the ComScore research shows how Facebook is focusing on generating revenues from advertising.

"If we think back a couple of years, large brands were hesitant to use social media channels. Fast forward to today, and that has really reversed itself. Almost 3 out of every 10 ads or so are on Facebook," said Lipsman.