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

When the series shifted from the WB to UPN for its sixth season, fans were treated to one of its most innovative episodes: the musical Once More With Feeling. Most prominently for Trachtenberg, whose ballet talents were showcased that week, she opens the episode’s coda, “Where Do We Go From Here?,” singing the opening title line a cappella.

Michelle Trachtenberg, the actress who rose to fame as a child star with films like “Harriet the Spy” and went on to have memorable roles on TV shows including “Gossip Girl,” has died, according to an NYPD source.