Blake Lively and Alyson Hannigan are among the former "Gossip Girl" and "Buffy" actors mourning the death of their one-time co-star, Michelle Trachtenberg.

Blake Lively is mourning the loss of her former Gossip Girl costar Michelle Trachtenberg after the actress’ death. “This is the first day I met Michelle. She was electricity,” the A Simple Favor star,

Blake Lively, Sarah Michelle Gellar, David Boreanaz, Ed Westwick, Kim Cattrall, Kenan Thompson, Melissa Joan Hart and more shared tributes to Trachtenberg.