Accumulate as much info as you can.
This will cost you money so you need to decide whether it's worth it or not.
You know what he looks like, so once you find out his where abouts, do some PI work (sitting in your car all day)
Chances are he trains...start by looking at all the possible gyms in the area.
Go to these gyms and try to find out if he is a member...(some people are easy to bribe...or you can fabricate a story)
If you see him driving a car take the license plate down...(if you have a line into that, that's all you need...somebody who can run the plates.)
Do you know any of his family members...that could be another way of figuring out where he is.
Once you have that info: Rent a Van with 2 sliding doors (tinted windows) 3 guys in the back seat, once he comes out of his car to get into his apartment, have the 3 guys snatch him and drag him into the van, 2 guys handcuff him in the back, and 1 drives. The one driving should have a handgun, make sure he sees it...drive to a predetermined location...and start asking him all the questions: where's the money...gear...blah, blah, blah. If he lies, crack him in the head. Make sure you have his cell phone, driver's license, and keys
At this point, there should one of your guys watching the scammer's apartment/parking lot) to ensure that no police are coming. After 20-30mins if all is clear, the driver will exit the van, with the keys and cell phone and go into another car. He will drive with another man to the apartment/house, you have to make sure nobody is home so make a call from the scammer's cell...(also at this point you should know if he has an attack dog or not.) The man who was watching the parking lot will come in with you. One has the gun(air clip), one has pepper spray (in case of a dog) Come in and go throught the place snatching anything you can find(money and gear, electronics)
Exit the house, go back to the van and drive up to an isolated area, the scammer gets out, you pistol whip him and then pretend to shot him execution style, take the handcuffs off...drive away
Obviously you have not used your real license plates through all this. Get out of his town, and put the old license plates on, Dispose of the stolen plates.
Chances are, he will pay you back.