Dyfed-Powys Police have named the missing boy who is believed to have gone into the River Towy near Carmarthen as 11-year-old Cameron Comey.
The youngster was last seen playing near the river in the Tanerdy area of Carmarthen with his brother, late on Tuesday afternoon.
Officer are urging anyone who was in the area of the river between 2pm and 4pm on Tuesday, February 17, and who have any information, to call 101.
The search and rescue operation is set to continue on the River Towy today, involving two dedicated swift water response teams from the Mid and West Wales Fire and Rescue Service.
The teams, from Carmarthen and Swansea, are made up of specialist search and rescue trained officers who use equipment such as specially adapted inshore boats and camera equipment that can assist with the search effort.
The Coastguard, an RAF Seaking helicopter and inshore lifeboat teams from Tenby, Llanstephan, Ferryside and Burry Port are also involved in the search with around 50 individuals taking part.
The police helicopter will continue to assist in identifying possible search areas.
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