Last food thief I dealt with, I just sent out a group email to the company at large:
"To whom it may concern,
That sandwich you stole out of the fridge and ate wasn't just any sandwich. I went to a lot of trouble to shoot that raccoon and, you know, ammo costs money, too. So, I'd appreciate whoever did it to at least comp me the price of the ammo. Thanks."
That stopped that food thief and also no one asked me to participate in the holiday potluck anymore, either. It was a win-win.