Sometimes, a friend may come along who isn't so hesitant about taking money, but hesitant when it comes to giving it back. All it takes is a firm reminder and a little patience!
Tell your friend that you will not lend anymore money until they pay the previous amount back. This is an effective way of getting it paid off, but they will just turn around and borrow money again, so it's half-and-half.
Remind them every 2-3 days for about a week. If they still haven't paid it back, move on to the next step.
Pull them off to the side and make sure neither one of you are distracted. Say something such as, "It's fine that you borrowed money from me, but I'm getting very impatient. I need that money and I'd like you to give it to me by (deadline)."
Be polite. You can be firm without being aggressive. Never, ever make intimidating threats such as "if you don't give me my money back, I'm gonna make you'".
Talk to them again after about a month, but this time, you must be a lot more firm! Raise your voice at them and tell them if they don't pay you back soon, you will quit giving them money. However, if your friend owes you large sums of money, wait to do this after about two months.
If over 3 months pass and your friend still does not pay you then let them know that you do not want to see them again until they pay you. However, don't think that the friendship is about money. Did you just give money to your friend just so they could pay you?
If you are still unsuccessful, accept the fact that you have lost your money for good and you have learned a valuable lesson. If it was a very large sum of money your last resort should be legal action.
If you are willing to use legal action be sure to have evidence that this is a trespass to title meaning that you gave your friend temporary title of the money instead of possession. Whoever has the greater right to title or possession will win. You will also have the burden of proof so be prepared. If you have any evidence at all that he knows he has the money and he will pay you back then that is your strongest piece of evidence.