If you're lucky, he might wait on you. Try to get as much interaction out of him as you can. For example, if he comes to your table to check on how things are, ask for a refill of coffee or iced tea. This will force him to come back to your table. If he doesn't work in a store, you can still stalk him.
Receptionists are notorious for leaking information.
For example, if you don't know his last name, call and ask for him by his first name. The receptionist will most likely ask for his last name. Pretend that you can't remember his last name and act really embarrassed about it. Drive by the place he lives. When I was a sophomore in high school, my friend Gretchen and I had a route that we drove daily that passed the houses of all the boys we liked - Chris Toupe, Geoff Henderson, and John Livingston.