The 18-year-old looked rested and happy in the clip, where she thanked fans for helping her get through "the darkest time of her life".
She said: "The journey that I have been on had been very, very difficult over the past few months.
"I was dealing with issues that I know not only girls just my age but of all ages are dealing with. People that are probably watching this video right now are dealing with the issues that I had to and I hope to one day raise awareness of everything.
"I can’t tell you how much light you guys brought into my life in probably the darkest time of my life. Without you guys, I wouldn’t be here today."
Demi checked herself into rehab last October, citing 'emotional and physical issues' after reportedly brawling with a dancer.