Dear Renee:
Yes, definitely, you need to use a live trap. If you can borrow one from an animal rescue group in your area that would be best as they will give you lots of helpful advice. The way you find these groups is to call a few vet clinics in your area and ask if they know of any groups doing cat rescue. Sooner or later, one of the clinics will give you a contact person and phone number. If you can't find any group close to you, your next bet is to open the yellow pages of the phone book and look up "pest companies". Often they will rent a trap to you so you don't actually have to buy one.
Hope you're successful - good luck -