Flames were reported at about 8:35 p.m. Thursday at the hillside mansion in the 4000 block of Sea View Avenue, said Brian Humphrey, spokesman for the Los Angeles Fire Department.
The homeowner, one of the house's 12 residents, was unaccounted for after tenants said he ran into the burning structure to rescue some puppies that were inside.
A 74-year-old woman was in fair condition following treatment for smoke inhalation, according to Humphrey.
More than 140 firefighters responded to the 9,111-square-foot home and knocked down the bulk of the fire after two hours and 47 minutes, the LAFD said. The smoldering mansion, constructed in 1991, partially collapsed Friday morning as fire personnel dealt with remnant hot-spots.
"Some of them were permanent rooms. Some of them were built after the fact," renter Aron Doughty said, describing the property. "My loft was awesome. There were some of the other rooms you couldn't pay me to live in."
Firefighters used three cadaver dogs Friday to find remains, but Los Angeles Fire Department officials said no remains were found. They were careful because they said the structure has been deemed unsafe.
Earlier authorities had said human remains were found, but have since recanted that information.
Neighbors said the police were frequently called the house because of problems.
City News Service contributed to this report.