What are some social networking sites (like facebook) popular in France?

I'm a French-Immersion student from Canada. I know French pretty well. However I only know how it's spoken in book. I know no slang. I'm going to be working in Paris over the summer in 2011. I was wondering what social networking websites are popular in French so my french can improve and I won't sound so Canadian and new when I'm over there.What are some social networking sites (like facebook) popular in France?
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