Hilchos Lashon Hara chapter 10, section 13
However, I think that if he reckons that by telling people how so and so did him a wrong in money and suchlike, benefit will result, it is permitted. For example if he speaks to people to whom the perpetrator will listen and return what he stole. Or to prevent the perpetrator from wrongly shaming him by telling important people or his friends the truth so that they stop him from doing it. Or if one was already shamed by him and wants to stop it happening again by telling his friends or important people. This is permitted because one’s intent is to defend oneself.