Robert Jensen and Carol King (two of the victims of Charles Starkweather/Caril Fugate).
Still wondering how the Lindbergh baby got to be a teenager, or what Justin Bieber song explains this mystery. 
Columbine
Stay current for maximum shock value
Go with Rehtaeh Parsons or Audrie Potts
Ennis Cosby was shot during an attempted robbery and was far from a teenager at the time.