Officers were called by West Quay security staff on Sunday, 23 April, after it was reported to them that a man had inappropriately touched himself whilst sat next to two young girls.
The incident happened between 2.30pm and 3pm on the second level of West Quay shopping centre.
The man is described as being around 5ft 5ins tall, possibly Middle Eastern, with short dark hair. He was wearing a blue jumper with a beige colour and dark blue jeans.
Anyone with information is asked to call 101 with reference 44230159015.
Alternatively, you can call Crimestoppers 100% anonymously on 0800 555 111.