I think it needs to be addressed whether these are 'linked' in a sinister way (for example a pact), or 'linked' in a far less sinister way, (young impressionable kids living in the same area).
Firstly, I'd really steer clear of the Bebo and Emo scare stories. Bebo is not much more different to Facebook, and not too far removed from AB, it's not some sort of underground cult where every kid with a profile is swapping suicide tips. Leave the Emo's alone, they're the angsty miserable teens, but a tiny fraction go in for self harm and suicide. If anything they're the most articulate young kids out there who will go on and do well in life.
Suicide in clusters is not a new thing
http://en.wikipedia.org/wiki/Copycat_suicide - this is a fascinating Wiki page.
You find that in an area where there are a few sudden suicides it can spiral out of control quite quickly, with teenagers especially given their unstable emotions and inability to deal with grief as well as others