The 13-year-old was forced into a cubicle in the toilets at British Homes Stores and raped in an attack that lasted several minutes. The attacker was eventually disturbed by another member of the public.
Yesterday, as police released a photograph of the suspect taken from security cameras, they warned that he was a danger to all children.
"It is extremely disturbing to me that this boy was actually raped whilst shoppers sat drinking tea and coffee in the store restaurant, just a few yards away from the toilets," said Detective Superintendent Eddie Hemsley of West Yorkshire Police.
"The man responsible for this sickening offence is a danger to children. Anyone who can commit an obscene act like this in a public toilet could clearly strike again."
The attack, on 7 August, took place at British Home Stores in Leeds. The teenager had left his mother, but arranged to meet her again later.
He had been washing his hands in a sink, when the man grabbed him and forced him into the cubicle.
The attacker was disturbed by a member of the public who entered the toilets and then chased the attacker, but lost him in the crowds of shoppers.
Det Supt Hemsley yesterday told a press conference that he believed the attacker had deliberately followed the boy into the toilets.
"He has been looking for his victim and was on the look- out for a young boy," he said.
A police spokesman last night said that the boy, who has received specialist counselling, appeared to be making a relatively good recovery after the attack. He did not suffer any lasting physical injuries.
"The trouble is that you don't know what psychological harm he might suffer - not just now but in years to come," he said.
The spokesman said detectives had been looking at both local and national paedophile registers, but had been unable to identify the attacker.
They remained convinced, however, that this was not the first time he has offended.
They have also spoken to other people captured on the security film and who had been shopping in the store.
British Home Stores last night refused to comment.