Two 13-year-old girls were walking along the railway bridge near Serpentine Road shortly after 2 pm last Wednesday, November 28, when they stopped to observe what was happening on the track below.
A white van then stopped and a male person, believed to be the passenger, spoke to the girls and took a photograph with a Polaroid camera.
Police are anxious to trace the man, who is described as being approximately 40-years-old and is mainly bald, but may have hair on the sides of his head. He is also described as being of medium build and is believed to have a local accent.
The vehicle he was in, which made off out of Tenby towards Kilgetty, was a large white van, which may have had writing on the sides and possibly building materials inside.
Police are appealing for anyone with any information about the incident to contact them at Tenby police station on 842303.