One of the stars ofBuffy the Vampire Slayer, and apopular presence in 90s films and TV shows, has died.TheNew York Postreports that Michelle Trachtenberg, who appeared for three seasons onBuffy as the title characters sister Dawn, and also co-starred on the original incarnation ofGossip Girl, has died. ThePostclaims, per police sources, that her death is not being investigated as suspicious. (TMZ reports that the cause [of her death] remains unclear.)Trachtenberg was only 39 years old.Born in 1985, Trachtenbergappeared on the Nickelodeon sitcomThe Adventures of Pete & Pete and done numerous commercials when she received her breakthrough role as the title character inHarriet the Spy.The film, based on the kids novel by Louise Fitzhugh, became a cult hit, and was the first film released by Nickelodeon Movies.READ MORE: The Best New TV Shows of the YearIn the year 2000, Trachtenberg joined the cast ofBuffy the Vampire Slayerstarting with the series fifth season. In the Season 5 premiere, Buffy vs. Dracula, Buffy suddenly has a sister Trachtenbergs Dawn even though the character had never been mentioned or appeared on any of the prior seasons. The mystery of Dawns true origin and the reasons behind her arrival became an ongoing mystery on the series.A few years afterBuffyconcluded, Trachtenberg became a recurring guest star on the originalGossip Girl, playing the manipulativeGeorgina. (Trachtenberg reprised her role on the recentGossip Girl revival as well.)AfterGossip Girl, Trachtenberg appeared on shows likeCriminal Minds, NCIS: Los Angeles, andSleepy Hollow, and hosted the Tubi true crime seriesMeet, Marry, Murder.TMZs report on Trachtenbergs death claims that in recent months, the former child star shared troubling social media posts, appearing gaunt and frail. In response, Trachtenberg insisted in other posts that she was happy and healthy.Whatever the circumstances of her death, this is a shocking loss. 39 years old is way too young to lose someone.The Best Movies of 2024Our editor and critics picks for the top 20 movies of 2024.Gallery Credit: Matt Singer