The Way rapper, 26, was dating Ariana Grande until earlier this year when they split. The rapper, real name Malcolm James McCormick, was found dead on Friday, police told the US website.
His cause of death has not officially been confirmed.
Rapper Mac hit the charts back in 2010 with his first single Knock Knock – and the star shared the stage with his then-girlfriend Ariana at the One Love Manchester concert last July in the wake of the terrorist attack last May.
“But beyond helping me launch my career he was one of the sweetest guys I ever knew. Great man. I loved him for real. I’m completely broken. God bless him.”
Shawn Mendes said: “Mac Miller truly was one of the greatest hip-hop artists of all time, always had passion towards doing something he always loved.
“My deepest prayers & condolences goes out to Mac’s friends and family at this difficult time. Life is too short.”
Rapper Wiz Khalifa added: “Praying for Mac’s family and that he rest easy.”
Lil Skies tweeted: “RIP Mac Miller…This hurts another legend lost…really inspired me coming up…I’ll never forget you an your impact..ever.”