You'll firstly need proper legal advice from a lawyer who has experience with legal battles related to cryptocurrency and get honest feedback on the chances of actually getting some or all of your outstanding investments back. Properly document all the information you have about the owners, your investments and your profits during the short time the project worked.
This by itself will cost some money and will basically be committing you to the recovery chase.
Are you aware of other investors who are equally interested in going down this road? If you all pool together the legal expense it will lighten the load.
I completely agree about the legal route, but not sure where to look for one.
I assume most investors only invested very small amounts and have since forgotten about it. I am yet to find another person, who is interested in pursuing this matter legally.