Snapchat: itstrinick
I don't know about any "poplular kids" but I just don't like it cause it has no advantage over skype or steam or texting.
I can't speak for Kik, but snapchat has one major advantage over anything else: timed photos. It's also a different environment than any other method of sending an image. With snapchat you send someone a picture and you don't expect a response. If you send someone a picture via text message, you're starting a conversation about that picture. You can send snapchats to 35 people and not have to deal with 35 people replying "Nice."