"A year ago today ... I was not in a good place," the 19-year-old said at her concert Saturday night. "I needed help and I want anybody in this audience to know that if you're struggling with one of the issues that I dealt with or a different issue, that you can get help, that you can recover and it's possible if you just tell someone."
Lovato entered a treatment facility for three months last year to deal with "emotional and physical issues." The singer-actress said as an 8-year-old who faced bullying she had an eating disorder and later started cutting her wrists to vent her despair.
She performed a show at New York's Hammerstein ballroom, just days ahead of the release of third album, "Unbroken."
Lovato was beginning to play her latest song, "Skyscraper," when she stopped to address the crowd.
"There are so many beautiful girls in this audience that don't know that they're beautiful, but they just are," she said. "So I want to thank you guys for being there for me every single day I was away. I wouldn't be here without you guys today."
Concertgoers screamed "I love you" while Lovato spoke and one girl held a sign that read: "Demi makes me strong!"
After performing "Skyscraper," she sang a cover of Lil Wayne's recent hit "How to Love," a song about women's insecurities and their struggles to find love.
Lovato was the star of the Disney Channel series "Sonny With a Chance" before she announced she was leaving the show in April.