The child, aged six or seven, is believed to have been put into a black Volkswagen van in Redstone Hill, Redhill, on Thursday afternoon.
The owner of a van pictured in a CCTV image circulated by police has been traced and ruled out of the inquiry.
Surrey Police said officers were treating the report with the "utmost urgency and seriousness".
A member of the public told Surrey Police they saw the boy being taken at 16:43 BST on Thursday.
Speaking at Reigate Police Station, Supt Chris Edwards said the young boy was seen at the roadside "tampering" with a small silver and yellow mountain bike, when he was approached by the van, near the train station, between 16:30 BST and 17:00 BST.
The witness described the child as being "taken from the roadside into a vehicle," he said.
A bike, believed to belong to the child, was left behind.
He added: "Anyone who knows anybody who has a vehicle that fits the description that was in the area yesterday, or if that was you, then please contact us immediately in order that we can establish the safety of that young child."
The child is described as white, approximately 4ft (1.2m) tall, and wearing a red T-shirt and navy blue jeans.
No parent has reported a child matching the description as being missing.
"We are treating the matter with the utmost urgency and seriousness as parents would expect us to do," said Mr Edwards.
The police helicopter based at Redhill has been involved in the search.
A large-scale police hunt is under way for a young boy who was reportedly seen being taken into a van in Surrey.