The young victim was riding on the canal path near Swine Lane between 4pm and 5pm on Tuesday when he was approached by six youths who demanded cash.
The youths ran off when they were then disturbed by a man, believed to be in a black VW Golf.
The boy was unhurt.
Detective Inspector Alan Flynn, of Bradford CID, said: "We are particularly keen to trace this person, who we believe was in a black Volkswagen Golf car, as they could have vital information which will assist in our investigation."
Five of the youths were described as white and one as Asian. They were believed to be aged around 13 to 14 years and were of average height and build.
One had short curly blonde hair, while the others had short fair hair. The Asian male had short black hair which was swept to the side.
All were wearing hooded tops and black trousers.
Anyone with information is asked to contact DC Asif Khan at Bradford CID on 101 or Crimestoppers on 0800 555111.