He had been expected to pick up his children on Sunday but failed to show up, prompting playwright David Katz and another person to go to his apartment, where they found him dead, CNN said.
Hoffman spoke in the past of struggling with drugs, including a 2006 interview in which he told CBS he had at times abused "anything I could get my hands on. I liked it all."
His death, if confirmed from an overdose, would recall the 2008 death of actor Heath Ledger, who was found dead in his Manhattan apartment from a lethal combination of drugs.
Born in upstate New York near Rochester, Hoffman won the Best Actor Oscar for the 2005 biographical film "Capote," in which he played writer Truman Capote. He also received three Academy Award nominations as best supporting actor, for "The Master" in 2013, "Doubt" in 2009 and "Charlie Wilson's War" in 2008.
After more than a dozen earlier roles, Hoffman burst onto the film scene in 1997's "Boogie Nights," in which he played a lovelorn gay man in a movie about the porn industry that helped make Mark Wahlberg a star.
PORTRAYED DISTURBING CHARACTERS
Hoffman, who brought a workmanlike intensity to his roles, often played characters with innate intelligence and logical minds riven by underlying passion. The blond, thickset actor's on-screen persona could range from professorial to unkempt, from the aloof intellectual to the everyman.
Hoffman appeared in blockbusters such as "Twister" and "The Hunger Games" series. But he was more often associated with the independent film world for his portrayals of often disturbing and complex characters in such films as "Happiness," in which he played an obscene phone caller, and "Before the Devil Knows You're Dead."
In the latter, he played a son who schemes to rob his parents' jewelry store, resulting in their deaths. Hoffman could also play nice, as in his portrayal of an angelic nurse in "Magnolia."
Other noteworthy films included "Moneyball," "The Savages," "Cold Mountain" and "Scent of a Woman," one of his earliest films, which garnered its star, Al Pacino, an Oscar.
Lionsgate, the studio behind "The Hunger Games," called Hoffman "one of the most gifted