'Celebrity Rehab' castmates Mackenzie Phillips and Lisa D'Amato also tweet about late ex-Alice in Chains bassist.

Mike Starr's friends and fans have taken to Twitter to express their grief about the ex-Alice in Chains bassist's death on Tuesday (March 8).

"Devastating to hear of Mike Starr succumbing to his illness," tweeted Dr. Drew Pinsky, who treated Starr on VH1's "Celebrity Rehab" and the spin-off show "Sober House." "So very sad. Our prayers are with his family."

Former Guns N' Roses drummer Steven Adler — another founding member of a hard-rock powerhouse whose career was sidelined by drug addiction — also hit Twitter: "R.I.P. Mike Starr!! Such a sad day! :( :(" Adler is also a "Celebrity Rehab" alum, though the two men appeared on separate seasons. Starr would have turned 45 next month.

"Drugs and alcohol aren't a joke," tweeted Velvet Revolver drummer Matt Sorum, who replaced Adler in GN'R. "Please take care of yourself and respect yourself. We lost Mike Starr today. Rest in Peace man."

Ex-Dream Theater drummer Mike Portnoy, who filled in with Avenged Sevenfold after they lost Jimmy "The Rev" Sullivan to an overdose, had this to say via Twitter: "RIP Mike Starr... I watched his struggle on Celebrity Rehab and had my fingers crossed for his recovery... this disease kills... sad stuff..."

Starr was found dead in a Salt Lake City house on Tuesday. He played bass for Alice in Chains from their inception in the late '80s until 1993, when he left the Seattle grunge stars while touring for their second album, Dirt.

Alice in Chains have several songs dealing with addiction. "You can't understand a user's mind," former singer Layne Staley sings on "Junkhead." Staley died in 2002 after overdosing on a mixture of heroin and cocaine.

Mötley Crüe's Nikki Sixx — a fellow hard-rock bassist who has made his own struggles with heroin very public (even calling his book and accompanying album with side project Sixx AM "The Heroin Diaries") — tweeted: "RIP Mike Starr. Another fallen Soldier to addiction... :("

"Mike Starr was a great and troubled guy," tweeted actress Mackenzie Phillips, who appeared on "Celebrity Rehab" with Starr. "I loved him. He would be so happy to know he's a #TT right now. Rest in Peace, brother. #dopekills"

Another of Starr's season-three castmates, Lisa D'Amato from "America's Next Top Model," tweeted: "My stomach is in my throat. We love U, Mike. #RIPMikey," with @ replies to Dr. Drew, Phillips, counselor Bob Forrest and Jennifer Gimenez, the actress known to reality-TV watchers as the house manager on VH1's "Sober House."

"I'm SHOCKED and SADDENED for the loss of MIKE STARR," Gimenez tweeted.

"Mike Starr was my homey," D'Amato tweeted a short time later. "He had a larger than life heart. My last visit w/him was a funny & sweet one. I'll always rmbr that. <3 #RIPMike."

"Mike Starr may you RIP," tweeted comedian Dane Cook. "Your music loves on forever."

Pro wrestler and hard-rock musician Chris Jericho tweeted, "Sorry to hear about Mike Starr's death. Amid all of the joking about tiger blood and winning, let's not forget that drugs kill people."

"Horrible news," tweeted Mark Morton, guitarist with heavy-metal band Lamb of God. "RIP Mike Starr."

Share your condolences for Starr's family and friends in the comments.