Officers are trying to identify a man who is said to have accosted a 16-year-old girl as she walked along a Scunthorpe footpath.
The incident happened at around 2pm on the Kingsway footpath between Brumby Wood Lane and North Lindsey College, on Wednesday, September 9.
The unknown man fled towards Brumby Wood Lane after the girl pushed him away.
He is described as white, in his 50s, around 5ft 7” to 5ft 8” tall, of normal build and balding, with grey hair around the top and sides of his head.
He was wearing black shiny tracksuit bottoms and a black zip-up jacket.
Chief Inspector Jenny Bristow said: “We would urge anyone with information about the identity of this man or men to come forward.
“Incidents of this nature are very rare. However, Humberside Police takes them seriously and is doing everything possible to catch the person responsible.”
Anyone with information is asked to call 101, quoting log number 291 of September 9.