put something in the Search field, hit enter.... when you get to the search page, you will see "Search Profile" next to the search bar... Click that, it will bring you to an advanced search, where you can search by multitude of criteria - hometown, interests...whatever. it searches within your networks, so it's good to join a network if you haven't yet (e.g. I joined "Slovakia" and "Boston University"). Also, you can go through friends' friends and see if someone you know pops up there.
I connected with over 20 classmates from primary school out of which i only kept touch with one over the years. we had a reunion recently...without facebook it would not have been possible. nifty at times.