Poser, follower, a charlatan of sorts. One who copies or immitates all or most of the aspects dealing with their idol. They may wish to have certain clothing, skills, vocabulary, etc., of their idols instead of their own. Most likely a wannabe is lacking in self confidence and is looking for guidance.

Someone who wants to be what they are not.

1. Someone trying too hard to fit in with a specific crowd of peepz. They usually change the way they act, dress and or talk.

2. A faker, a poser

(A.) Someone who wants to be something else and fit in a crowd, someone who tries to act like someone they want to be even though it's obvious that they're just a stupid wannabe.

a person who acts like someone that they are not. also see moron

Desperate person who wants another persons identity so does a pathetic impersonation lame

Another person trying to imitate another. Most of the time for "popularity" or to get rid of their insecurity.
Wanna be Goth, Wanna be Prep... etc.