Police sources said Haim's mother was with him at his Oakwood apartment and called 911 after finding him unresponsive, according to TMZ.com.  The Los Angeles coroner's office said Haim died at Providence St. Joseph Medical Center in Burbank. The actor was taken by ambulance to the hospital from an apartment in Los Angeles.

The LAPD said his death appeared to be an accidental drug overdose, and an investigation is underway. The coroner's office said an autopsy will determine the cause of death.

Haim is most famous for his roles in the 1980s films "Lucas" and "The Lost Boys." Haim and Corey Feldman starred in several popular films together, including "License to Drive" and "Dream a Little Dream," and became one of the hottest young actor teams in Hollywood.  Haim's drug use took over his life, however, and helped ruin his career.

"I feel like ... I ruined myself [with drugs] to the point where I wasn't functional enough to work for anybody, even myself," Haim said in an interview in 2007.

The actor was involved in several projects at the time of his death, including the film "The Science of Cool" with actress Mischa Barton, due out in 2010, and "The Dead Sea," which is currently filming.