Legal Question in Credit and Debt Law in Nevada

Possibly. If it was entered without duress or coercion, expresses the essential terms of the agreement (how much money, what payments, interest rate - if any, responsible party for payment, time for repayment), and is signed by the party to be charged. So, if your debtor signed the IOU (promissory note) and it contains the essential terms, it is probably as legally enforceable as any formally drafted contract between you.

Now, collecting on it may be another matter - particularly if it is not secured by any property you can repossess for payment. Chase him down and make your demand in writing ... and if he does not perform, take him to small claims court and have a judge tell him he has to pay his debt.