Before you decide to sue someone who owes you money, you should understand that attorneys will not take such cases for a percentage of the settlement unless the case is very clear and the amount of money owed quite large. You could easily end up not getting your money and having to pay the lawyer as well.
Make sure that you have proof before you go to court. A signed agreement, voicemail, text message, or another person that was there when the money was exchanged. You don't want it to come down to your word against theirs.
Consider the money you loaned to your friend if it is worth what you will pay a lawyer to sue him Find too if you can settle your matter through arbitration. Make sure you have proof that you loaned your friend money. Otherwise, consider negotiating a barter type of payment arrangement if your friend does not have the money.
You should firstly know that the friend has the means to pay what is owed. Litigation is pointless when you are incapable of collecting on a judgement. Second you would need to know that there is some proof of the loan being made. Third you would need to know what the Local Legislation says.