Michelle Christine Trachtenberg TRAK-tən-bərg (born October 11, 1985) is an American actress. She is best known for playing the lead role of Harriet M. Welsch in Harriet the Spy, Nona F. Mecklenberg in The Adventures of Pete & Pete, Dawn Summers in Buffy the Vampire Slayer, and Georgina Sparks in Gossip Girl.