A blind woman was sexually assaulted by a man pretending to be a "good Samaritan" who helped her disembark a Northern Line train at Waterloo.
The woman was riding on the London Underground with her guide dog on 3 December shortly before 10am when the man offered to help her.
But the pervert sexually assaulted her before running away.
Another passenger on the southbound platform then helped her to the ticket hall to report the incident.
Detective Constable Suleman Yazdani said: "The man who committed this offence masqueraded as a good Samaritan, purely so he could take the opportunity to sexually assault his victim.
"We work extremely hard to make sure the Tube is a place where women can travel without the fear of unwanted sexual behaviour and are determined to find the person responsible for this assault.
"Who is the man in the picture? I think he has information which can help us."
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference TSUB/B6 of 26/01/2015.