The family has been passing out fliers in the Rockridge neighborhood and asking for the public's help.
The focus of the search returned to the Rockridge area Thursday afternoon. Police sent 30 officers back into the neighborhood to visit homes and businesses they may have missed in the past couple days.
The boy's faster father, Louis Ross, says the boy was last seen in the parking lot of a shoe store where the boy's foster mother, Jennifer Campbell, works.
Police say they still have eight detectives working full-time on the case, including one from the homicide division.
The FBI and Fremont police have also gotten involved, searching the family's home in Fremont and towing Ross' BMW. According to police that car has now been returned to him.
"We have not spoken to the media up until this point, not because we were shy or we're hiding," said Ross. "We're with the police and FBI giving them all the information. First day alone, we were with police for 17 hours straight."
"He has taken a polygraph but he didn't tell me what the results were, but he did tell me he spoke truthfully, answered all questions, but I haven't spoken to anyone about it," said attorney John Burris.
Police will not confirm whether Ross took or passed the polygraph.
ABC7 News has learned that detectives have visited an auto salvage yard in Hayward over the past two days. Employees there say Ross was there before the boy disappeared on Monday, and that the boy waited in the car while Ross searched the yard for car parts. Police confirm that they have been searching in that area as well as many others. They have also searched a levee behind the salvage yard.
Police have clarified that the boy is disabled, but does not wear leg braces, but instead wears orthotics inside his shoes. He is able to walk, although with some difficulty.