I had a surprise party held for me once at East Side Mario's. Basically it's a popular Italian resturant with a younger age group crowd that serves, pizza pasta, unlimited salad and garlic bread!! They have amazing desserts too. I highly recommend it if there is one by you!
I would also recommend any buffet style resturant. They are laid back, upbeat and you can eat as much as your hearts desire.
I personally love larger resturants that are a bit louder and upbeat for a celebration.
I work at a resturant which is laid back but relaxing. Tons of teens go there and celebrate their birthday because we are famous for our deserts.
Any place with good deserts, a younger age group and an upbeat setting would be the place to go!