A 17-year-old girl from the Buckingham area was sexually assaulted on a bus in Milton Keynes last Wednesday.
A witness appeal has been launched and police have released CCTV footage of a man they would like to speak to in connection with the assault.
The teenage girl boarded the X5 Stagecoach in Buckingham, bound for Bedford.
At 1.37pm a man boarded the bus outside McDonald’s in central Milton Keynes.
After speaking to the girl for about 30 minutes, he moved to sit next to her.
He then touched her inappropriately and asked her questions of a sexual nature.
The girl got off the bus at Bedford bus station. The offender followed her off the bus but is not believed to have followed her after this.
The man shown in the CCTV picture is black, aged in his late 20s, of medium build and around 5ft 8in tall, with a tidy black beard.
He was wearing a black leather jacket, a blue V-neck jumper with buttons at the top, cream chinos, and brown leather shoes.
If you recognise the man or have any information about the incident, contact investigator Selena Nolan on the Thames Valley Police non-emergency number, 101.
If you don’t want to speak directly to the police you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org