The search for a seven-year-old Japanese boy missing since his parents abandoned him in a bear-inhabited forest was proving frustratingly difficult due to a lack of clues, a rescuer said Tuesday, according to AFP.

As the search continued for a fourth day on Japan's main northern island of Hokkaido, two hunters joined more than 100 rescuers, police and local town officials after they found fresh bear droppings in the area, heightening concerns for the safety of the child.

But they have found no clues to the whereabouts of Yamato Tanooka, who has been missing since Saturday after his parents made him get out their car on a mountain road as punishment for misbehaving.