United Kingdom, Feb. 27 -- Taylor Momsen's "heart is on the floor" after Michelle Trachtenberg's death.

The 31-year-old actress and singer - who played Jenny Humphrey on 'Gossip Girl' - has paid an emotional tribute to ler late co-star, after she was found dead this week aged 39.

She wrote on Instagram: "In shock. When I met this girl 17 years ago I knew we'd be friends.. she was smart and sassy, bold and sensitive, funny as f*** and filled with fire. 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 fri...