If he works in a shop, I would go there. Something could have happend to him or he have another sim card or what ever.
If he has a store, someone knows where he is. You have the receipt?
Then I would go to the police, if you cant find him.
If nothing helps and he just sold it or something, then it´s up to what makes you feel good. But If you pay someone you dont know to visit him. Then you dont know whats gonna happend, or when it´s gonna stop.
The other man can easily pay double so the violence commes back to you. It´s all about money. And only one is gonna benefit from this. Thats not gonna be you.
Do it your self, maybe ask/pay a freind to go with you, as a support. If you dont wanna do it, dont do it.
Better to loose one 414 then one 414, alot of money and getting badly beaten.
Hope everything works out.