We talked about your story with my family, may we ask if you are a boy or a girl and if you are bar/bat mitzvah. And again we would be very happy to send you 50$, which actually, I suggested even before talking to them. See, I once was an unpaid shomeret for a chiloni (it was cash in a purse) and it was stolen under my eyes and I did not even notice or realize – I was so shocked, it must have been a skilled thief – I offered to pay the money, especially since I saw he had a very upset face, but he refused, said the halacha is not so (a chiloni, let me remark again); I replied I wish to give as a gift, but he told me he does not even want to hear about it and left. In case he reads YWN and recognizes the story, I have set the money aside for him and either me or my children / grandchildren will discuss it with Eliyahu Hanavi in good time.
Back to your story, it does not work to call, say, my rabbi. Only your Rabbi can pasken for you, and even if he could not be available for whatever reason, another Rabbi has to know who is your Rabbi before he can decide.
One solution which I was taught, if you do not wish to talk to a Rabbi and tell the story, is that, regardless of what the halacha is, you restore the 50$ whether you are obligated or not, with the intention that if you are not obligated, it’s a gift, and the intention you don’t consider it tzedaka, just a gift you are willingly giving to – whomever. (I assume you are bar or bat mitzvah.) Of course in a similar way, someone can send you the money, willingly and in good heart as a gift to whomever (perhaps to you, perhaps to the thief, perhaps to the teacher, perhaps to your friends who gave for the gift, or to anyone else), we give it away forever because it makes us happy to do so.
The other option is that you tell all the facts to your father or to your rabbi, both about the stolen money and about the availability of cameras, and all other details, and then you do what they tell you.