Effectively, there is nothing you can do. This was an unsecured loan, you cannot collect if he doesn't pay. You can try to sue him, and you may win, but then you'd have to enforce the judgment and you'd have to sue him wherever he lives. Unsecured lending is high risk; that's why credit card interest rates are usually ridiculous 15-30%. You can literally max out a card, never pay it back and have zero liability to the bank that issued it to you. If banks cannot do anything, neither can you - at least not legally.
Give it up, move along and consider this your tuition fee.
That is exactly what I meant with this post.
Your best chance of getting the money back is by praying. There's no guarantee that he repays it, and as you can see in his profile, in all 70BTC worth of loan, there were 15 late payments.
The first rule of giving a loan: Consider the cost! Interest doesn't and won't matter if the cost is too high because the one who requested the loan will probably not have enough money to pay it back.