The woman was travelling on the 423 bus towards Norwood between 7am and 8am on September 14 when a man boarded the bus and sat next to her.
He made a number of inappropriate comments towards her before touching her thigh, police said.
The incident was reported to police the next day and an investigation was launched.
PC Charlotte Joseph, from the Met’s Roads and Transport Policing Command, said: “This was a really frightening and intimidating experience for the victim, which has left her nervous to travel.
“The suspect thought it was fine to harass, and grab a woman who was simply going about her day. It is absolutely not acceptable that any woman should have to deal with this type of behaviour and we are working hard to identify the man responsible.
“We have conducted a number of enquiries since the incident was reported, including looking at CCTV, speaking with witnesses and facial recognition."
Police have urged anyone who believes they recognise the man in the image to come forward.
Anyone with information is asked to call 101 quoting CAD 1779/15Sep.
