West Yorkshire Police said the man is reported to have been called Terry and was thought to have had the nickname ‘Walrus’.
He is described as being white and was believed to be in his thirties or forties at the time of the alleged offence.
He was of large build with a ruddy complexion and had grey/silvery hair and a beard.
He was believed to live in the Keighley or Skipton areas at the time of the alleged offence.
Detective Inspector Ian Cottrell, of Bradford District Safeguarding Unit, said “We have carried out a number of enquiries to establish the identity of this man and are appealing to the public to contact us if they can assist us in this matter.”
Call police on 101, quoting crime reference 13180366687.
Information can also be reported anonymously to independent charity Crimestoppers on 0800 555111.