Some (Facebook) friends of mine started a facebook group. They spent a few months developing it. Then one of the administrator accounts got hacked. The hacker then deleted all the other administrators, thereby seizing control of the group.
There is no way to contact Facebook that I know about, and Facebook states in their FAQ that that will not help you here.
If an unauthorized person gains admin status, we encourage you to contact them directly to resolve this matter. Unfortunately, Facebook is not able to reinstate you as an admin for any group or Page.
In essence they are protecting the hacker and refusing any help to those that suffered the loss.
Furthermore, Facebook states that the Original administrator of a page or group cannot be removed. Well, they can. Here is a video illustrating it. I wonder how many hours were lost by honest people who were compromized by hackers?