• by Mark Walsh  @markfwal, December 3, 2012

Pinterest ranks as the fastest-growing social network this year, with its U.S. audience surging more than ten-fold to 27.2 million between July 2011 and July 2012. To put that in perspective, the next closest social property among the top in terms of growth was Google+, which increased 80%, according to new data from Nielsen and NM Incite.

Facebook, of course, remained by far the largest social networking site, with monthly PC-based traffic of 152.2 million, but that figure was down 4% from a year ago. No. 2 ranked Blogger saw traffic dip 3% to 58.5 million, while traffic to No. 3 Twitter was up 3% to 37 million. LinkedIn’s traffic was flat at 28.1 million.

Visually-oriented Pinterest was also the fastest growing property on the mobile side, with mobile Web visitors up a whopping 4,225% to 14.3 million, and up 1,698% to nearly 5 million through its mobile app. As on the desktop, Facebook had the largest mobile audiences, at 74.2 million on the mobile Web, up 85% from a year ago, and at 78 million from mobile apps, up 88%.

Nielsen said total time spent on social media in the U.S. across PCs and mobile devices increased 37% to 121 billion minutes in July 2012, up from 88 billion in July 2011. People also spent more time on social networks than on any other type of sites—roughly 20% of their total time online via PC, and 30% of time in mobile.

Pinterest's rapid growth helped it raise $100 million in May led by Japanese e-commerce company Rakuten, giving the startup a reported valuation of $1.5 billion. The site has also become a magnet for brands and publishers and Pinterest recently introduced new business accounts and tools for companies to capitalize on that interest.