I agree. Your nephew has stolen something valuable from you. He needs to get Aaron back right now, or you should press charges. This is thoughtless, criminal behavior. What did he need the money for, anyway? Drugs? Why would a 17-year-old need money desperately enough to break someone's heart without caring? It is cruel to you, and even more so to Aaron, taken from a safe home where he is loved to who-knows-what kind of care?

Do you know any cops, or have friends who do? Perhaps an "unofficial" visit from a cop, who would then accompany him to the third party's place to retieve the poor moneky, might be the answer. If that's not possible, then the police should be notified, ASAP.