Sarah Michelle Gellar, Taylor Momsen and Blake Lively mourn death of Michelle Trachtenberg

Sarah Michelle Gellar, Taylor Momsen and Blake Lively are among those paying tribute to Michelle Trachtenberg, who died Wednesday. Trachtenberg was found in her New York apartment “unconscious and unresponsive,” according to an NYPD statement. She was 39.

“Michelle, listen to me. Listen. I love you. I will always love you. The hardest thing in this world, is to live in it. I will be brave. I will live… for you.” — ”Buffy the Vampire Slayer" star Sarah Michelle Gellar via Instagram.

“Everything she did, she did 200%. She laughed the fullest at someone’s joke, she faced authority head on when she felt something was wrong, she cared deeply about her work, she was proud to be a part of this community and industry as painful as it could be sometimes, she was fiercely loyal to her friends and brave for those she loved, she was big and bold and distinctly herself.” — Blake Lively, Trachtenberg's ”Gossip Girl" co-star, on Instagram.

“Rest in peace sweet Michelle” — Kim Cattrall on Instagram.

“I’m heartbroken to hear of the passing of @michelletrachtenberg!! So young, so talented and so sweet!” — Melissa Joan Hart, who shared a scene with Trachtenberg on "Clarissa Explains It All," on Instagram.

“She was simply awesome. I’ll miss our late night calls that no one should ever hear but us. She was always in my corner and there to support me whether I was right or wrong. I will miss you everyday my love.. I think we truly understood each other and I am so grateful to have had a friend like you in my life for so long.” — “Gossip Girl” co-star Taylor Momsen on Instagram.

“Michelle was one of a kind. I remember her coming on set for the first time and just absolutely owning it. She was a force of nature and just so so unapologetically funny and magnetic.. remembering those years with a big smile. Just a terrible loss. Love you.” — “Gossip Girl” co-star Chace Crawford via Instagram.

“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. 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.” — “Buffy” co-star James Marsters via Instagram.

“What a terrible shock and loss, my god. My heart aches for your mama. Fly safe little bird.” — Kate Beckinsale via Instagram.