According to a story in Washington Times:

http://www.washingtontimes.com/news/2011/apr/23/sex-trafficking-us-called-epidemic/

From the story:

“We know it is a really large number,” said Anne Milgram, a former high-ranking federal prosecutor who tried and oversaw sex trafficking cases. “We know there are a lot of children being victimized. We just can’t tell you what number.”

The story seems to be mostly about girls. But in it's purpose it intends to include boys.

Allen