While I am sure a few of them are, I don't think a lot of these girls are wearing those clothes when they leave the house. When I was a teen (17/18) I would change in the back seat of my friends car when we went out. I had a job and paid for the clothes myself and my folks never knew I had them. Now, keep in mind that I was just wearing skirts and/or Goth (we didn't have that word in the early 90's) type clothes. I wasn't walking around mostly naked showing off everything I had and I certainly wasn't at a mall. I was just wearing clothes my parents didn't approve of (they hated me wearing all black).
Personally, I blame Britney Spears and the like for this new line of prostiteens that we have walking around. While I doubt many have the....um.....courage to do it, I think that a few people should walk up to these girls and ask them, "How much?" just to see what they say. Maybe getting confused for an actual hooker a few times will change their minds about what they are wearing.