If you are a teen with bladder control problems maybe you shouldn't be going to a sleepover unless all of your friends are aware and accept your problem. If you really want to Depends is an adult brand diaper that might be suitable for you.
The best diaper for teens to wear is a brand called Tena.Discount stores also have offbrand diapers that work just as well in keeping you dry and feeling cofident and secure.
Tena and Depends are easy to find adult diapers that have smaller sizes. Pampers makes a teen diaper, but it's hard to find so you may have to order online.