Hollywood is mourning actress Michelle Trachtenberg, who died on Wednesday. She was 39. Trachtenberg, best known for roles in "Buffy the Vampire Slayer," "Gossip Girl," Disney's "Ice Princess" and more, is believed to have died of natural causes, police sources told ABC News. Since the news of her death broke Wednesday morning, many of her friends and former co-stars have paid tribute to the late actress on social media. Read more: https://abcnews.visitlink.me/2h15-7