Net income in the first half of 2011 came to almost US$500 million, according to the source, who wished to remain anonymous because privately-held Facebook does not disclose its results.

Facebook's stronger results come as investors have pushed its valuation to roughly US$80 billion in private markets, with many industry observers expecting the world's No. 1 Internet social network to go public in 2012.

Its growing popularity among its advertisers and 750 million users has pressured entrenched Web companies such as Yahoo Inc, which ousted its chief executive Carol Bartz on September 6.

Search leader Google Inc launched Google+, a rival social network in June that attracted more than 10 million users in its first two weeks. Google is trying to increase the appeal of its social network by offering games such as Zynga Poker and Rovio's Angry Birds.

Some venture capitalists and industry experts see early signs that Google+ is headed down the right path in taking a bite out of Facebook.

Facebook earned US$355 million in net income in the first nine months of 2010 on revenue of US$1.2 billion, according to documents that Goldman Sachs provided to clients during a share offering this year.

The source did not provide figures for a direct comparison for the first half 2011 figures.

Created by CEO Mark Zuckerberg in a Harvard dorm room in 2004, the company is expected to introduce new features this month such as music services from Spotify and Rhapsody, according to people familiar with the plans.

Facebook has become one of the Web's most visited destinations by people who spend hours on the site every month sharing photos and videos, and conversing with friends.