Humberside Police has issued a warning after a spate of robberies reported last week in the Newland Avenue and Cottingham Avenue areas in the city.
Most of the reports say that two men on a moped mounted the pavement and tried to snatch mobile phones from people's hands.
The robberies occurred between December 7 and 9, and police believe bicycles have also been stolen.
One of the men was wearing a red striped jacket and red helmet, a spokesperson for the force said.
The spokesperson added: "Until we can find who these people are and arrest them we are appealing for people to be extra vigilant and keep their mobile phones and bags secure."
Police today released a blurred CCTV image of the suspects.
Anyone with information is asked to call police on 101, quoting log 178 of December 8.