The way law help you take action is you go see an intellectual property lawyer who has experience in software, copyright, trademark and patent law and discuss the specifics. You should have a case, and perhaps a substantial one as you seem to have proof that this was deliberate.
There are a lot of good software IP lawyers in Palo Alto and in Silicon Valley, so find one and ask for a free initial consultation and go from there.
So far, this is free to you. Until you pay a fee, I am not your lawyer and you are not my client, so you take any free advice at your sole risk. I am licensed in IL, MO, TX and am a Reg. Pat. Atty. so advice in any other jurisdiction is general advice and should be confirmed with an attorney licensed in that jurisdiction.
Your fact description is not sufficient to provide you advise. You need to consult one of the many fine IP attorneys in your area. The answer depends on the facts, amongst other things, and what you may think it stolen property may or many not be so.
USPTO Registered Patent Attorney, Master of Intellectual Property law, MBA I am neither your attorney, nor my answers or comments in AVVO.com create an attorney-client relationship with you. You may accept or disregard my free advice in AVVO.com at your own risk. I am a Patent Attorney, admitted to the USPTO and to the Florida Bar.
I'm not at all sure you're right to conclude that the software was "stolen." The other folks who helped develop the software [by which I take to mean they wrote some of the code] are, absent an agreement otherwise, joint authors of that software and are, therefore, co-owners of the copyright in that software. Again absent an agreement otherwise, any of those co-owners may lawfully sell copies of that software. Their only requirement is to pay you a pro rata share of the revenue earned from the sale. You've concluded that you've been wronged somehow but I'm not all sure that's true. You need to speak with your own intellectual property attorney.
The above is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
Possession of stolen property can be a criminal offense in most states. But I would need to know much more before I could conclude that "x" was in possession of stolen property. I agree with Daniel----if you developed the software with others, and if there was no written agreement among the authors of the software defining how their ownership interests would be divided and administered, then each of the owners has the right to license the software even without consent of the other co-authors. Just because you told "X" that you were cheated does not make that so.