I think I'm missing something here... Why would a scammer buy advertising for your site?
What have you done to try to get the identity of the scammer? (Ask the networks politely?) The networks are obviously getting money, so they're most likely not going to do anything they don't have to do.
If you're serious about taking action, hire a lawyer and get a subpoena. Faced with real legal action (and penalties if they don't comply), the networks will probably give up the goods pretty quickly at that point.