The suspect is alleged to have exposed himself while travelling on a 94 bus in Holland Park Avenue, Kensington and Chelsea on Saturday November 9 last year, at 7:50pm.
The following week, on November 16 at 4:20pm, he was reported to have inappropriately touched a 26-year-old woman on a route 27 bus in Euston.
DC Staniland said: "Unwanted sexual behaviour on the transport network is not tolerated and all sexual offences are taken very seriously. I would like to remind everyone, but women in particular, to always report incidents of this nature to the police. If you have any information please dial '101', but in an emergency always dial '999' immediately."
Officers are treating the incidents as linked. The suspect is described as a white male, approx 35 years, medium build and approx 6ft tall.
Officers have released CCTV images of the suspect and anyone with information is urged to contact DC Lucy Staniland who is leading the investigation on 020 7421 1074 or Crimestoppers anonymously on 0800 555 111.