Over the past month, Trachtenberg has posted a few photos on Instagram, including a few throwbacks. Her most recent selfie appears to have been uploaded on Wednesday, February 12.

Actress Michelle Trachtenberg’s death was ruled “undetermined” Thursday morning after her family objected to an autopsy, according to a spokeswoman for the city medical examiner’s office and

Sarah Michelle Gellar mourned the death of “Buffy the Vampire Slayer" co-star Michelle Trachtenberg in an Instagram post.

Hollywood is mourning actress Michelle Trachtenberg, who died on Wednesday. She was 39. Trachtenberg, best known for roles in "Buffy the Vampire Slayer," "Gossip Girl," Disney's "Ice Princess" and more, is believed to have died of natural causes, police sources told ABC News.

Sarah Michelle Gellar, Taylor Momsen and Blake Lively are among those paying tribute to Michelle Trachtenberg, who died Wednesday.

Several actors, including Blake Lively and Melissa Joan Hart, have paid tribute to Trachtenberg after she died on Wednesday.