I know personally of two cases very much like what Dave is describing, both involving boys who in the past had been brutally abused both physically and sexually.
In one, the kid ran into a group of older guys who made him feel special, wanted and important. But one part of being "cool" was that he should carry drugs for them, and of course he didn't understand that he was just being used as their "mule" - when the inevitable bust came, he was the one caught holding, not them. Not to mention the exposure to the drugs themselves: 13 and already experienced with LSD and heroin.
In the other case, the kid's a skater who fell in with a group of older skaters who, again, made him feel appreciated and important. They got him into hard drugs for a laugh, and then, when he started to become dependent on the drugs, they demanded payment, which he didn't have because he was only 14. So they agreed to "accept" sexual favors instead. He figured it didn't matter, because he had already done all these things so many times in the past anyway.
People who are willing to do this to kids really are the scum of the earth.
Nobody living can ever stop me
As I go walking my freedom highway.
Nobody living can make me turn back:
This land was made for you and me. (Woody Guthrie)