The most recent one that I can talk about was a predator who was using a popular weight loss forum to prey on girls by standing in as a "personal weight coach." Another case, a month or so ago, it was a guy who started out on facebook, but took things to skype pretty quickly after that.
In both cases, the fact that the girl was using a laptop (and also their phone) allowed the predator to manipulate the girl much more effectively.
SD3, this stuff gets dark as shit really fast. We have to review all/most of the evidence prior to trial. Those are not good times. It's not something I really like to talk about a whole lot when I don't have to.
I don't think you are going to prevent this kind of stuff by limiting access to technology - that is pretty much impossible these days. The only defense is making sure your kids are educated and appropriately fearful.