You can call the police to find out how little they care about kids stealing Pokemon from one another. You're better off calling Officer Jenny.
- Put in place policies to help prevent theft
- If theft still occurs, be more strict
- If you catch the person stealing, punish them and make an example out of them. Kick them out for a month -something like that.
If you suspect someone, or have a clear picture as you put it, interview that person and get to the bottom of it. If they are doing it, but don't admit it, the heat can be enough to make them stop. Don't be timid about it, either -problems don't get solved by waiting for them to happen again.