Buffy The Vampire Slayer and Gossip Girl actress Michelle Trachtenberg has died aged 39.Her death is not being investigated as suspicious, police sources confirmed to the New York Post.Trachtenberg was best known for her work as Buffy's (Sarah Michelle Gellar) younger sister Dawn Summers in 66 episodes of UPN teen supernatural drama Buffy the Vampire Slayer spanning 2000-2003.