"As you can imagine, s--t is just f--d up right now," wrote the hip-hopster on the Beastie Boys' blog. "But i wanna say thank you to all our friends and family (which are kinda one in the same) for all the love and support. i'm glad to know that all the love that Yauch has put out into the world is coming right back at him. thank you."
Horowitz also put up a picture of a hand with the colored marker inscription "PWR2MCA I♥U."
His remembrance is the first public comment on the loss of MCA from the group other than posting Yauch's obituary on their website.
It follows a flood of heartfelt dedications pourin in the last three days from fans and fellow artists who were shocked to hear the MC had lost his nearly three-year battle with cancer.
"The Beastie Boys were one of a kind! And so was Adam! They were all an important part of my musical history and integral to the musical revolution that was happening at the time. I'm very sad to hear about Adam's passing. God bless him and his family."
The Red Hot Chili Peppers honored Yauch by covering "So What'cha Want" and "Gratiude" off the Beasties' 1992 album Check Your Head at a concert in Newark on Friday.
"We lost a good man today," frontman Anthony Kiedis told the crowd. "He left the world a lot of beauty. I hope you carry that flame. Adam was for real."
And he'll be missed.