Hasanni Campbell was last seen Monday night in Oakland's Rockridge neighborhood, where his foster father took him to see his foster mother.
Police say Hasanni's foster mother's fiance dropped the boy off at a shoe store where the foster mother works at about 4:20 p.m. He left the boy in the car and walked to the storefront to unlock the door, but when he returned, Hassani was gone.
FBI agents on Tuesday searched the Fremont home where Hasanni lives with his foster father and his aunt.
Hasanni's grandmother, Pamela Clark, said that about six months ago, a court removed the 5-year-old and his sister from their mother's home but she wouldn't say why.
Clark says the court then gave legal guardianship of the children to Hasanni's aunt and her fiance. The family says the arrangement was agreed upon and there are no custody issues.
Hasanni has cerebral palsy and wears braces on his legs to help him walk. His family says he has been making a lot of progress in physical therapy lately but they are worried about his health and special needs.
"He's only five years old. He does have some special medical conditions that need to be attended to on a consistent basis." The boy's godmother, Regina Douglas said. "The people who have him now may not have that information."
Family members on Tuesday passed fliers out with pictures and description of Hasanni in hopes it will help them reunite with the boy.
Police say they have interviewed Hasanni's biological parents, who live in San Francisco, and are keeping all investigative leads open.
Hasanni is African American with brown hair and brown eyes. He is about 3 feet tall and weighs 40 pounds. He was last seen wearing a gray sweatshirt and gray pants. He wears leg braces that have Spiderman on them.