Renfro died Tuesday at a Los Angeles apartment where he spent the night with friends, Craig Harvey, chief investigator for the Los Angeles county coroner, tells PEOPLE.
Renfro was heard snoring overnight, but found not breathing later Tuesday morning, and the friends called 911. Paramedics declared him dead at the scene at about 9 a.m., Harvey says.
A cause of death was not immediately determined, but Renfro had a history of drug problems.
Drug overdose is a "possibility considering his history, but right now all we have is the history of his drinking the previous night," Harvey says. "All that we have is that he was last known to be alive during the morning hours and he was snoring."
The actor, who starred in The Client and Apt Pupil, had recently completed a movie with Winona Ryder and Billy Bob Thornton.
Film director Joel Schumacher discovered Renfro at age 12 and cast him in the 1994 John Grisham movie The Client (which also starred Susan Sarandon and Tommy Lee Jones). The following year, PEOPLE named the young screen hopeful one of its "Top 30 Under 30." The actor's other credits include Tom and Huck, Ghost World and Deuces Wild.
But Renfro had a troubled life off-screen, going back to 1997 when he was sentenced to two years of probation after he tried to steal a yacht.
In 2005, Renfro was busted again, this time in a police sting in which he was charged with a felony count of attempting to possess heroin. In a separate incident, he was charged with a misdemeanor count of driving under the influence and two counts of driving with a suspended license.
In January 2006, he entered a rehab program. At the time, Renfro's attorney, Richard Kaplan, told the Los Angeles Times that his client was doing well and "looks forward to doing whatever is necessary to take care of his personal and legal issues." Renfro eventually plead guilty to the heroin charge and was sentenced to three years' probation.
Most recently, in June 2007 Renfro was found to have violated his probation by not enrolling in a long-term drug treatment program. A judge warned him that if he violated probation two more times, he could be sentence to a live-in rehab program or to jail time.
Renfro's death was first reported by TMZ.com.