Sarah Michelle Gellar and Michelle Trachtenberg. Photo:
Sarah Michelle Gellar/Instagram
Sarah Michelle Gellar is mourning the loss of Michelle Trachtenberg.
On Thursday, Feb. 27, the day after the actress was found dead in her apartment, Gellar, 47, paid tribute to her with a carousel of photos from their time on Buffy the Vampire Slayer together.
“Michelle, listen to me. Listen. I love you. I will always love you,” Gellar wrote of Trachtenberg, who was 39, quoting her character’s last line from the series. “The hardest thing in this world, is to live in it. I will be brave. I will live… for you.” She added “💔💔💔🗝️” to the end of the caption.
Trachtenberg joined Buffy as Dawn Summers, the kid sister to Gellar’s Buffy Summers, in season 5. Her existence in the show was explained by her being a mystical “key” put into a human body and sent to the Slayer for protection against the evil god Glory (Clare Kramer).
She stayed on the show through its finale in 2003, but Gellar sacrificed herself in the season 5 finale — and told her sister, “Dawn, the hardest thing in the world is to live in it. Be brave. Live — for me.”
Michelle Trachtenberg, Sarah Michelle Gellar and Shannen Doherty. Sarah Michelle Gellar/Instagram
Trachtenberg was found “unconscious and unresponsive” in her apartment around 8:00 a.m. on Feb. 26, the NYPD confirmed to PEOPLE. She was pronounced dead at the scene and an investigation remains ongoing, but criminality is not suspected, per police.
A source told PEOPLE that the Gossip Girl actress was “really down emotionally” and had been dealing with “health issues” over the last year.
“She told friends she was struggling. She was really, really sick and open with those in her circle about how much she was struggling,” the source said.
Sarah Michelle Gellar and Michelle Trachtenberg. Sarah Michelle Gellar/Instagram
In the aftermath of her death, several of her Buffy costars have paid tribute to her memory.
David Boreanaz was among the first cast members to react to the news online, writing on his Instagram Stories, “So very sad …horrible news. RIP and prayers to her and her family.”
James Marsters, who played the vampire Spike on the show and shared many scenes with Trachtenberg, said in a statement shared with PEOPLE: “My heart is heavy today. We have lost a beautiful soul.”
“Michelle was fiercely intelligent, howlingly funny and a very talented person. She died much too young, and leaves behind scores of people who knew and loved her,” he continued. “My heart goes out to her family, who are good people and are suffering the greatest loss anyone could bear. I hope everyone can give them space to heal in this most difficult time. Godspeed Michelle. You are missed.”
Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories.
Alyson Hannigan, who starred as Willow Rosenberg on Buffy, also shared a touching tribute on Instagram, writing, “I am deeply saddened by the news of Michelle’s passing. She brought a loving energy to the set of Buffy. My thoughts are with Michelle’s family and friends.”