A 70-year-old woman was pushed to the floor and had her bag snatched in Todmorden.
The victim was on Lloyd Street between 8.30pm and 9pm on Friday when the thief attacked.
The man officers want to speak to in connection with the theft is described as in his mid 20s, white and slim. He was wearing dark clothing.
Any witnesses are asked to contact Detective Constable Craig Aubrey of Calderdale CID on 101.