You would need to file a claim with the court. The many experts on here can explain that process.
In regard to the rings, I recommend you report that to the Police as soon as possible. With any luck, they'll catch up with him before he sells them.
Also, treat this as a life lesson. The golden rule is "There are no friends in business." So whenever considering helping out friends in ways like this, think beforehand about what you might have to do if things don't work out. Never help if you are not willing to pursue them and lose the friendship (and possibly others) over it. It may sound cynical, but that's reality. You are more likely to be shafted by a friend than someone you don't know.