Years ago we had someone stealing sandwiches from the office fridge. One of the ladies put a note on her sandwich saying "I spit on this sandwich." The thief left a note that said "so did I."
We had a flower fund that we all contributed to every pay day. When an employee finally died, there was no money in the fund. Nobody knew anything about where the money had gone.
We also had a coffee fund. Everybody was supposed to put a dime in the can when they had a cup of coffee. The money disappeared regularly, and we were always out of coffee. One morning someone came in early and caught the culprit. It was one of the supervisors; nothing was done about the problems.
As long as the thief leaves employee stuff alone, it is up to management to catch the culprit and deal with the situation. They may just choose to ignore it.