Hollywood is paying tribute to Michelle Trachtenberg. The actor who starred in 'Harriet the Spy,' 'Buffy the Vampire Slayer' and 'Gossip Girl' died at 39.

Cast members of "Buffy the Vampire Slayer," "Gossip Girl" and more are remembering their co-star Michelle Trachtenberg​ after the news of her death.

O’Donnell was Trachtenberg’s A-list co-star in Harriet the Spy, the 1996 kids movie that marked Trachtenberg’s first major film role (she was just 10 when filming began). O’Donnell played “Ole Golly,” a nanny and mentor to Harriet, the precocious snoop and writer played by Trachtenberg.