"I dont know what to say Mac Miller took me on my second tour ever", tweeted Chance the Rapper.
He was found around noon at his Fernando Valley home and pronounced dead at the scene, reports said.
In May, shortly after the end of his two-year relationship with the pop singer Ariana Grande, Miller was charged with a DUI after police said he hit a utility pole with his auto. Just last month, the Los Angeles Attorney's Office officially charged the rapper with driving under the influence (DUI), stemming from a vehicle accident in May in the San Fernando Valley.
Miller and Grande broke up earlier this year, after dating for two years, according to media reports. "It's just a part of something that's going to continue to help make me who I am".
Grande then added: "I am not a babysitter or a mother and no woman should feel that they need to be".
Miller had long struggled with substance abuse issues.
And he told Complex in 2013 that negative reviews of his 2011 studio album "Blue Slide Park" - which debuted at the top of the Billboard 200 chart - caused him to become addicted to the antihistamine promethazine, also known as "lean".
Many fans in his native Point Breeze said Miller was taken far too soon.
The rapper and producer, whose given name was Malcolm James McCormick, was 26 years old.
He told Rolling Stone at the time: "Have I done drugs?"
A representative for Miller did not respond to requests for comment and Los Angeles emergency services declined comment.
Posting an image of the pair on Instagram, Sheeran said Miller's untimely death was "so heartbreaking".
"He was one of the sweetest guys I ever knew, "the rapper wrote on Twitter. [He] really introduced me to newer hip hop, something that I did relate to", said fan Gino Lagamba". It was like: "diet, carrots [then] Mac Miller", he laughed to Vulture in one of his final interviews.