Daniel Handley disappeared after leaving a friend's house where he had spent the afternoon playing. He had been reluctant to go home.
A search by more than 100 police officers yesterday failed to turn up any clues to the whereabouts of Daniel, of Lobelia Close, Beckton, east London. Police dogs and helicopters were involved in the operation, carried out on overgrown wasteland around the old Beckton gasworks near the boy's home.
Daniel is believed to have played there before and police said other children had built dens in the area.
Police divers were called in to drag a lake in Beckton Park, but last night the search was moving on to the Royal Victoria Docks, once used as a set for the Stanley Kubrick film Full Metal Jacket.
'We will continue to look for Daniel and we have to cover every possibility,' a police spokesman said. 'But I'm afraid that time appears to be running out for him.'
Superintendent Ed Williams, leading the search, said: 'It would be foolish to dismiss the idea of an abduction. We have serious concerns for his health. With the cold weather over the last few days we are increasingly concerned.'
Daniel's mother, Maxine Handley, said: 'You never know just what it feels like until it happens to you.'