I remember seeing this when 1985(my birthyear) was still an underage one. I've actually tracked kids down like this myself - for their own safety. I worked with youth online, and often with serious problems. There were a few times when I looked for information like in this story to track down suicidal kids and get their info to their local authorities. A very fast-paced and somewhat thrilling experience, which seems odd to say, but it's so amazing how the bits connect - of the times I tried to track suicidal kids down, I'd guess it worked for about half.
-Now imagine a pervert doing this, instead of a helpline worker... bad news.

I would guess that about half the youth online leave enough information to track them down - based on what I've seen.