How much was the loan? what it over $500? do you have evidence of the loan? check with a notation that it was a loan? emails between you and the borrower?
If it was a loan for over $500 you will need some sort of paper trial to evidence the existience of the loan. If you have this then you should be able to recover it in a lawsuit.
You can certainly file a lawsuit against the person. The court where you file is determined by the amount of the debt involved. A key component, as pointed out, is whether it was a "loan" or a "gift." Evidence of prior payments, the existence of a written agreement, or written promises to pay, are critical.
But then, after you win, comes the really hard part, collecting money from someone who does not have any.
I am not your attorney unless you and I have signed a retainer agreement. What I am saying is not legal advice. Do not act on this information without engaging my services, this is for consideration only.