1. Find a lawyer who is tech-saavy (a lawyer specializing in Technology).
2. Call lawyer, inform the lawyer of information that can be made available (his Safe-Mail e-mail address is a good start here)
3. Ensure you have proof that a contract of some sort was breached (his PMs and his thread ought to suffice).
4. Provide this to information to the lawyer
@ this point the lawyer should be able to elaborate on the next steps which would be:
5. Police report
6. Culminate all information into a court order/subpoena - issue this to SafeMail requesting every IP address associated with this account.
It is VERY likely that he is using Tor/VPN, but also very likely that he slipped up somewhere.
Do some digging in the IP trail; find one that doesn't bring you to a VPN / Tor node.
Use aforementioned information to subpoena/court order this ISP. Get account holder name.
At this point -> local PD.
Account holder will probably deny involvement.
This is where your lawyer / PI will help you.
Cost for subpoenas are about $0 - $10.
Information to issue one could be between $0-$1,000.
Total process could be quite a bit, depending on how involved your lawyer is.
THE POINT here is that if your lawyer thinks he can track this person down and reclaim some money, he will do it because it's possible and it's in his/her best interest.
I am pursuing a Law Degree in Technology, but this information is purely from an amateur perspective.
You can find this guy because I guarantee that at some point in his quest, he fucked up.
Unfortunately Bitcointalk isn't of help. I bet those alt-accounts of his possess more information than AvalonShenzhen would like.
Your right safe-mail will have his real ip when first sign up, after that they can change settings.
But his real name is not possible, unless the IPS is willing to give that. Maybe ask someone in Israel?