You can write off the loan as a bad debt on Sch D of your income taxes if you have the documentation showing that it was a true loan. That means that your IOU must show the amount borrowed, an interest rate, and the anticipated repayment schedule (ie what the monthly payment should be). You also need to have documentation that attempted to collect the debt and were unsuccessful - normally in the form of certified letters.
If the loan documents are in good order but you do not have the certified letters, you can do that now. Show a pattern of trying to collect for at least 6 months and then you could write it off as a bad debt.