I disagree my teenagers had mobile phones their girls and I like the fact there safer when walking too and from school or out with mates if they carry one, its a quick call to me or someone, same if routines change.Social media I find if used in the manner intended is fine, as you say parents should take an interest also i woukd argue its not the tool it's the user.
Look at the gun dispute in america as an example.
One more thing who's to say this didn't happen more often in the past these days with more news coverage more stories are being broadcast.