The boy was mauled while paddling in the sea at Southend, Essex. Despite public appeals, the owner, who was walking two dogs at the time of the attack, has not come forward.
The boy was with his grandmother when one of the dogs ran into the water, grabbed him across his chest and back and forced him under the water on Eastern Esplanade on August 5.
His grandmother managed to pull the boy from the dog's jaws and both dogs and their owner ran on to the promenade.
Officers have also released an e-fit image of the man they would like to speak to in connection with the incident.
Pc James Crabb said: "This was a horrific incident and it is almost impossible to imagine how anyone can watch a child being so severely mauled before simply running away.
"It is possible of course that the dogs weren't his and he was walking them for someone else, so please don't be put off from coming forward if he looks familiar but isn't a dog owner.
"If you are the dog walker we are looking for, or if you have stayed silent to protect him or the dogs, please think again. Look at this boy's injuries and think how lucky he is that he wasn't even more seriously injured, thanks only to the intervention of his grandmother."
The boy's mother, who does not wish to be identified, said: "These dogs are aggressive and dangerous and their owner is clearly careless and irresponsible.
"I have no doubt that my son's life was only saved due to the brave and rapid reactions of my mother-in-law. It is vital that this man is caught and that he is brought to justice for his crime. It is very difficult for us as a family to put this violent incident behind us, knowing that this man is still at large."
(This is Guernsey - November 21, 2011)
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