We all know that MySpace and Facebook are the two most popular social networks, but which are the fastest growing social networking sites? Compete.com has released their listing of the twenty most popular social networks, and these are the big winners in terms of growth:

1. Ning.com with 4,803% growth
2. Twitter.com with 4,368% growth
3. Yuku.com with 1,400% growth
4. Linkedin.com with 729% growth
5. Myyearbook.com with 284% growth

Ning was the big winner, but Fubar.com was also impressive with over three million percent growth over last year. Of course, when you only have around 200 monthly visits the year before, it makes it a little easier to post such a huge number. I did not list them in the top five because of that low number last year, but gathering over 6.5 million monthly visitors in a year is still very impressive.

Facebook was also a big winner. They only had 77% growth, but that growth amounts to around 140 million visits a month.

The big loser? Xanga. The social blogging network was down 66 percent.

For those interested, you can view the full list of the top twenty social networks at Compete.com.