No, there isn't one. Don't worry.  And rightfully so!  There isn't a social network just for lawyers, and frankly I think lawyers should stay off social networking sites in general.  While it's important to make sure your acquaintances know what you do, it's even more important that you avoid potential conflicts of interest.

I recently noticed a friend of mine who recently became a lawyer who has been adding people a lot lately.  I asked, and as I suspected, he's been adding some of his new clients.  Obviously he should be paying more attention to this, as some of them can't know about each other!

This is not to say that lawyers are precluded from networking professionally with other lawyers.  Sites like LinkedIn.com or Probook.ca for Canadians are great.  There's nothing wrong with meeting other lawyers and forming professional relationships.  In fact, it's key. 

Just make sure that to your clients, you're not an internet-addicted social climber.