Volunteers, family and police are spreading fliers around to help find the missing boy.
Despite two days of exhaustive searches, 5-year-old Hasanni Campbell is still missing.
Hasanni was last seen Monday in Oakland's Rockridge neighborhood, where his foster father took him to see his foster mother at the shoe store where she was working.
Police say Hasanni's foster father, Louis Ross, dropped the boy off at a shoe store at about 4:20 p.m. He left the boy in the car and walked to the front of the store to unlock the door, but when he returned, Hasanni was gone.
Ross told NBC Bay Area that he and the boy's foster mother, Hasanni's aunt, are fully cooperating with police. While they have not hired a lawyer, they have sought advice from well-known civil rights attorney John Burris.
Burris said he told Hasanni's foster parents that they really should do what police ask.
"I impressed upon them how important it is to cooperate with the police. The police have a very important job here." Burris said. "You were the last person to see this child and quite reasonably they're going to focus on you, that happens all the time."
Ross told NBC Bay Area by phone that he had nothing to do with Hasanni's disappearance and that he and the boy's foster mother have agreed to take lie detector tests.
Ross took the polygraph test Wednesday night but the foster mother, Jennifer Campbell, is pregnant and didn't want to take the test for fear it would harm her unborn child, the Chronicle reported.
Police are not commenting about the polygraph test.
Oakland police searched Joaquin Miller Park but have not said yet if they were looking for anything specific or how close they were to finding the boy.
Police towed the car Hasanni was in the day he disappeared but have not said yet whether they have found anything important to the case. FBI agents on Tuesday searched the Fremont home where Hasanni lives with his foster parents.
Hasanni has cerebral palsy and wears braces on his feet to help him walk. The prosthetics, adorned with Spiderman logos, would not be visible because they are fitted just for his feet. While he can walk, Hasani's disability prevents him from running or jumping.
The National Center for Missing and Exploited Children has also joined the search.
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.