Yep. And kids aren't going to think of that angle because they don't know any better. A predator may have lived in a town for 20 years, but never acted out because public stalking behavior is too risky. Now these freaks can stalk from the privacy of their own homes, and appear in a public place only long enough to snatch the predetermined victim. Plus, the pool of stalkers has expanded out to as far as they are willing to drive.
I've explained this stuff to my kids, and I think it has really helped curtail the teen tendency of "knowing" everything about the world. They realize that the world can be a weird, hostile place and mom's knowledge is very useful. They don't care much for the internet anyway, as they have better things to do.
From what my kids tell me, these young girls will go on myspace (not saying that Kelsey did) and divulge all kind of information such as “I’m going shopping at —— right now, be back later!”
All parents should be discussing this with their children, as you have.