An eight-year-old girl was indecently assaulted by a teenage boy while walking home from a park.
The girl was approached by a teenager aged about 16 to 18 who took her to a lane and touched her inappropriately and tried to kiss her, police said.
The girl was playing in the Hill Street area of Penygraig, Rhondda, on Friday when the incident occurred.
Officers described the boy as white, slim, with ginger hair and freckles. He was wearing dark clothing.
The girl went home after the incident, which happened between 1930 and 2000 BST, and told her mother what had happened. She was left "upset and frightened", South Wales Police said.
Det Sgt Phil Simmonds said: "We are appealing for the public's assistance in identifying this individual who has touched the girl inappropriately and tried to kiss her.
"She was not injured in any way but naturally was upset and frightened by what had taken place.
"We wish to advise parents that this has happened but also reassure them that incidents such as this are rare and that we are doing everything we can to trace this individual."
"I would urge anyone who recognises him from the description, or who thinks they might know who he is, to contact us immediately."
Anyone with information is asked to call Ton Pentre police station on 01443 743828 or independent charity Crimestoppers on 0800 555111.