say that when someone calls and asks for an employee, if they hang up they have to report it. Then ask the 'perp' to state their name and the 'relationship' with the to the employee (father, brother, friend...). My guess is that this will freak the guy out and scare him away. Seriously, knowing that someone knows their number may cut things off quickly.
The police will probably do nothing with the info, but it will be on record. Maybe reverse steps #1 and #2.
Note: I did advertising at the Daily Universe when I was at BYU. I once used the artwork of several women for a promotion. I got a couple calls asking who these girls were. I just said that I didn't know – which was the truth. Also thought it was creepy. I wouldn't have given any names out anyway.... and this was in the early 90s.