Raymond Southall, of West Bromwich, West Midlands, disappeared shortly after fishing with his father Dean, 31, at the Billing Aquadrome leisure park, Northampton, on Thursday afternoon.
More than 100 police officers searched the 235-acre park throughout Thursday night and yesterday.
Raymond's mother, Sharon Southall, 31, and his grandfather, also called Raymond Southall, 52, appealed for help in tracing the boy.
The holiday park, which houses about 1,000 caravans, is built on the site of old gravel pits and contains about 12 leisure lakes or ponds. It is bordered by the River Nene.
Chief Superintendent Bob Thorogood, who is leading the investigation, said the area was a "nightmare" to search.
He said police had unearthed no positive sightings of Raymond since early yesterday afternoon.
Raymond's family said the boy had been fishing with his father near the family caravan at a small pool on the park.
At about 2.30pm he left his father, saying he was cycling to his grandparent's caravan, about two minutes ride away, to get another fishing rod. He was not seen again.
Raymond's grandfather said members of the family spent about four hours searching before calling in police.
Mr Southall, a steel worker, said of his son: "He would not let anyone take him. He has been brought up not to talk to strangers."Reuse content