The 27-year-old singer-and-actress says addiction is "no joke" after one of her pals, Thomas, passed away on Tuesday night (08.10.19) due to the "terrible disease", and his death has left Demi "crushed".
She wrote on her Instagram Stories: "Please hold your loved ones tight. Tell them they are special and that you love them. Make sure they know it. RIP to my boo @sirtruss.
"Addiction is NO joke.. heaven gained this beautiful angel last night because of that terrible disease. I'm crushed and will always miss you @sirtruss. (sic)"
Following Thomas' death, Demi - who has previously battled addiction issues herself - called for people to "ask for help" if they or someone they know is "struggling".
She added: "If you or someone you know is struggling please know it's okay to ask for help. (sic)"
Demi suffered a near-fatal overdose in July last year, and spent time in a treatment centre for addiction.
A month later, the 'Sorry Not Sorry' hitmaker broke her silence for the first time since she was admitted, and thanked her fans for their "positive thoughts and prayers".
She wrote: "I have always been transparent about my journey with addiction. What I've learned is that this illness is not something that disappears or fades with time. It is something I must continue to overcome and have not done yet. I want to thank God for keeping me alive and well. To my fans, I am forever grateful for all of your love and support throughout this past week and beyond. Your positive thoughts and prayers have helped me navigate through this difficult time. I now need time to heal and focus on my sobriety and road to recovery. The love you have all shown will never be forgotten and I look forward to the day where I can say I came out on the other side. I will keep fighting. (sic)"