Leaving aside the racial aspects of this, why would a teenager think that an older man who was following him was "creepy"? Because he thought he was gay. And that puts a different complexion on his murderous attack on Zimmerman.
See "Creepy:" Was Trayvon Martin Trying To Commit A Gay Bashing When He Attacked Zimmerman?.by Steve Sailer, May 19, 2012, in which Sailer wrote:
The media originally pumped up this story under the mindset that, of course, a black child would be terrified of roving white racists like George Zimmerman. I mean, aren't we always looking for an example of an evil white male attacking unprovoked a 17-year-old black male for white racist reasons?
But, what if it wasn't about race? It always made far more sense that if Trayvon was acting perfectly innocent and feeling perfectly innocent (i.e., not casing houses to break into and not looking to score drugs), then the youth was most likely experiencing fear and loathing of a man he suspected to be gay.
Gays have been known to target minority youths: see my own post Destroying What's Left Of Hispanic Family Values, about the movie Quinceañera, in which Carlos, a 20-something (for legal reasons) youth is seduced into three-way sex with his landlords—who evict him and his family when they tire of him:
Uncle Tomás’s landlords in the mixed Los Angeles neighborhood of Echo Park are a gay Anglo couple, James (Jason L. Wood) and Gary (David W. Ross), with whom Carlos is soon involved in three-way sex. "James and Gary, they love their Latino boys," Carlos’s Hispanic predecessor in their bed tells him.
So, yes, if you're a teenage boy and a strange man speaks to you on the street, you're entitled to suspect him of trying to pick you up. You are not entitled to leap on him and try to smash his head into the pavement.