The Los Angeles County Sheriff's Department held a news conference Monday morning asking for the public's help. Investigators say the victim, Bruce Bodel, was walking late at night near the intersection of Lycoming Street and Penarth Avenue when he was hit.
The driver did not stop to render any aid and took off, authorities say.
Bodel was taken to the hospital with major injuries, but he did not survive.
His niece attended the news conference and asked for anyone with information to come forward.
"This has devastated my family. He always liked to go for walks. He enjoyed going out into the community and supporting it in every way he could. So anybody who could help bring my uncle justice would be greatly appreciated," Jessica Bodel.
The suspect's car is described as a silver two-door sedan with front end damage and a cracked windshield.
Investigators at the Walnut/Diamond Bar sheriff's station can be reached at 909-859-2817 or anonymous tips can be phoned in to Crime Stoppers at 800-222-TIPS (8477).
City News Service contributed to this report.