I think a lot of teenagers find their tumultuous emotions that they experience at that age as very frightening and confusing and foreign. With the availability of information on the Internet, it's easy for people to find information and find others like them... but on the flip side, it's also easy for people to find information they shouldn't necessarily have. Being a teenager is really defined by not knowing who you are, so DID seems like the perfect label for "I'm a teenager and I have no idea who I am so I will be all these different people!". Teenagers especially want something that makes them seem different and mental illness is "trendy". It's unfortunate, but what can you do. I think it's fine to explore yourself and who you are, even if what you think turns out not to be true later on. So whether or not you have DID, you don't really have to prove it, you just gotta go with what makes sense to you. Those other people will get bored and move on at some point.
Err, I hope that makes sense, I am obviously speaking from personal experience here.