Let me see if I have this right. A rather seedy looking man that you don't know paid your friend $750 to introduce him to you. Your friend did not share any of this money with you or offer to share it, or otherwise compensate you for whatever you might do with or for the seedy guy. The seedy guy suggested that the two of you take a trip together, and you assume that he anticipated having sex with you, perhaps on the trip. You did not go, did not agree to go, did not go, did not negotiate any alternate "deal" with the guy, and did not have sex with the man. You accepted no money or anything of value from him.
If this is accurate, no crime has been committed, and the police are not going to do anything other than suspect that you have been involved in some kind of con game or something bordering on prostitution. My guess is that if you attempt to "report" this to the police, all you will get is aggravation.
I suggest that you question your "friend" closely as to what he said to the guy that made him think it was worth paying $750 to be introduced to you. After all, if your friend convinces somebody else, he'll have another $750, and you will be just as upset a second time.
Somehow, I suspect that there is more to the story, but that is as much as I can tell you, based upon what you have told me.
Good luck, and please click on "accept."