Allow me to clarify the legal issues at play here, even though I'm not an attorney.
1) You cannot sue him for gambling winnings. At best you can sue him for a refund of your total deposits minus total cashouts.
2) He committed a criminal offense by running the PPPoker club. You can report him for that.
3) He did violate the 1961 Wire Act by transmitting real money over state lines for purposes of gambling.
4) He also committed federal wire fraud if he accepted funds across state lines for purposes of gambling, with no intention to pay winnings.
I would attempt to report this to both local authorities and the FBI. Don't bother with the local authorities if you're in a relatively small city, as they won't know what to do with it, but perhaps they can help you reach the FBI.
It is actually a lot tougher to reach the FBI than you think. Due to the overwhelming number of people who go to the FBI over untouchable matters such as Nigerian internet scams, they make it tough to contact them. You're probably going to be stuck reporting this online:
https://www.wikihow.com/Report-Illegal-Gambling
Definitely report him. Do NOT be afraid that you'll get in trouble. You won't.
It will probably result in nothing happening, but if you pool together the biggest victims and can show $100,000+ of stolen funds, you might get their attention.