Detectives are appealing for information following an allegation of indecent exposure at a bus stop in Danemead Grove in Northolt.
The offence occurred on Thursday, 20 November at approximately 03:00hrs after the female victim got off a route 140 bus on her way home from work. The suspect is alleged to have approached the 27-year-old and offered her sex; when she refused he exposed himself.
The victim ran away towards Reading Road but the suspect caught up with her by grabbing her hands. The victim managed to free herself and escape, receiving assistance from two passers-by.
The suspect is described as being of Middle Eastern appearance, of slim build and aged 20-25 with black hair. He was wearing a black padded jacket with a hood.
Officers from the Roads and Transport Policing Command (RTPC) investigate. No arrests have been made.
Detective Constable Naomi Goodman, of RTPC, said: "I am very grateful to the members of the public who assisted the victim and would very much like to hear from them or anyone with information relating to this incident."
Officers have released a CCTV image of the suspect and ask anyone who recognises him or has any information to contact DC Goodman on 07770 315 678 or via 101. Alternatively, they can call Crimestoppers anonymously on 0800 555 111.
Unwanted sexual behaviour on the transport network is not tolerated and all sexually motivated offences are taken very seriously.
Always report incidents of this nature to the police. If you have any information please dial 101, in an emergency always dial 999 immediately.