It's not financially worth it. You might not never know the exact source--most will go by nicknames and even then you don't know if that's the source or not.

A lot of times piracy exchanges hands so often that it just gets to be too convoluted. Person A releases it but person B modifies it and rereleases it. Person C downloads it, modifies what person A AND B did and releases it. So on and so forth.

You can attempt to contact IF you think you know (some will include their own readme with their URL/group name in it) but most of them will just ignore you and/or feel even more inspired to keep taking your work.

I just think you should stop worrying about piracy at this point because you're not going to save the world of it. It's disheartening yes.. but you have to come to terms (as sad as it is) that piracy WILL happen to you. It's just a matter of you having the funds to "battle" it.

I would spend some time here and there reporting files that are copyright to you but don't spend any more time than necessary. You have a more pressing issue to pay attention to--your own product!

So support your product, provide updates, provide support.. keep your paying customers satisfied. That's your main goal.