Top social networking sites in US in February 2007’s audience grew just 4% in February 2008 from February 2007, whereas second-place Facebook’s more than doubled, growing 102% year over year, according to Nielsen Online. LinkedIn, meanwhile, increased its unique audience a whopping 271% year over year, reaching 7.4 mln in Feb., compared with 2.0 mln a year earlier – and challenging fourth-place Windows Live Spaces. MySpace’s unique audience totaled 55.4 mln in February, more than double Facebook’s 20.0 mln.