Officers from British Transport Police were called to the railway line close to Llanelli station at around 5pm last Friday (18 August) after reports of a casualty on the tracks.
Officers say they attended the incident, alongside paramedics, but sadly a person was pronounced dead at the scene.
The death is not being treated as suspicious.
The casualty was identified as 17-year-old Joshua Dyer.
His mum, grandmother and cousins said: “We will never know what went through Joshua’s mind, as he made the choices he did, but we do know the world is missing a beautiful and unique mind.
“Joshua is in no more pain now and is at rest.
“He was a wonderful and considerate son, grandson and nephew.
“He is deeply loved and missed.
“Joshua did not feel he belonged and wanted to be free of pain and worry. Fly high Joshua, our beautiful boy”
(Lead image: Family photo)
