Michelle Trachtenberg, who rose to fame as Buffy’s younger sister, Dawn, in the dark, comedic series “Buffy the Vampire Slayer” and as a conniving socialite on the show “Gossip Girl,” has died, according to the New York Police Department. She was 39.

The department said in a statement that officers, responding to a 911 call just after 8 a.m. today, found Trachtenberg unconscious and unresponsive in a Manhattan apartment. She was pronounced dead by emergency medical workers, who had also responded.

The medical examiner will determine the cause of death, the department said, adding that criminality was not suspected.

Beginning as a child, Trachtenberg had a long list of credits in movies and television that endeared her to a generation of fans.

In 1996, she portrayed Harriet Welsch, a precocious 11-year-old who meticulously records her observations of neighbors and classmates in “Harriet the Spy,” a movie based on Louise Fitzhugh’s beloved 1964 children’s book of the same title. The movie also starred Rosie O’Donnell as Harriet’s nanny, Ole Golly.

Trachtenberg also portrayed Casey Carlyle, the heroine in the 2005 figure-skating movie “Ice Princess.” Other credits included the 2004 raunchy teen comedy “Eurotrip” and the 2009 comedy “17 Again,” which also starred Zac Efron and Matthew Perry.

This article originally appeared in The New York Times.

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