Kato Toshio, 85, lives at the Arcadian Residential Community at 24647 Mohr Drive and walked away from the care facility around 5 p.m. Monday, police said.
Toshio is considered at-risk as he has Alzheimer's disease and other medical conditions. He has walked away from the facility one other time, but was quickly found, police said.
Police said Wednesday they had followed several leads without locating Toshio. Local police agencies and hospitals have been notified about his disappearance.
The investigation indicates foul play is unlikely, police said, and to help the search, police have released a photo of Toshio.
Arcadian Residential Community and Toshio's brother have pledged $7,000 for information leading to Toshio's safe return, police said.