All depends if the person lives in the US, ive had people cut and run with 10's of thousands and tried to contact their law enforcement and was in these word:

We do not recognize this online currency we can't and will not waste resources for something that holds no real physical value.
I was then informed of other channels we could try and use but they all basically said the same thing. Most European countries are this way.





I live in a state were it is legal tender so if they also lived in my state its considered a currency.
The cash proofs is enough but the legal fee's dealing with someone outside the US isnt worth it and your better off taking it as a 4.5k investment in knowledge.

But if they live in the US sue them im sure you can find someone online that can find you all the info you need.