Crowd source this problem. Add a report fake account option. If so many (x) number of different IP address, etc. report it, sandbox that account. Simple.
If I were the adversary, I would respond by dedicating a fraction of my fake accounts to reporting thousands of random Facebook users. Gum up the system.
If I were the adversary, I would respond by dedicating a fraction of my fake accounts to reporting thousands of random Facebook users. Gum up the system.