"Youths" snatched cash from a pensioner on a mobility scooter who had just used a cash machine in Hull on Christmas Day.
The 89-year-old man had taken a number of notes out of the ATM outside Sainsbury's on Greenwood Avenue around 9.30am when he was approached by two boys on bikes.
They grabbed the money from him before riding off along 26th Avenue, police said.
The man, who was on a mobility scooter, was not hurt.
Police are treating the offence as a robbery, they said in their appeal.
The youths have been described as white and in their late teens. One was wearing dark blue clothing and riding a distinctive lime green mountain bike.
The other was wearing a khaki green coat and blue jogging bottoms and riding a silver mountain bike.
Anyone with information is asked to call 101, quoting log 127 of December 25.