The numbers are in, and LinkedIn is tearing up the race track.

MediaPost is reporting that among the top social networks, LinkedIn was the fastest-growing over the last year, according to October ratings released Wednesday by Nielsen Online.

"The site geared toward professional users drew 4.9 million visitors last month, up from 1.7 million a year ago. Other fast-growing social networks included kiddie site Club Penguin, up 157% to 3.8 million users, and Facebook, more than doubling its audience to 19.5 million in the last year. MySpace remained the top social network with 58.8 million users, up 19% from 2006."

Note that MySpace and Facebook both have comprehensive mobile components, which are available on different handsets and carriers to varying extents. LinkedIn has no mobile component yet.

MediaPost went on to report that among blog services, Blogger was the top one in October with 34 million users, followed by WordPress.com at 11.4 million and Six Apart at 10.6 million.

Linked-In: Fastest-Growing Social Network [MediaPost]