The police said one of those missing had contacted his relatives on Sunday evening and informed them that the group had lost their way, reports Xinhua news agency.
The trekkers are all residents of Homagama town and had ented the mountain range on April 6.
The Knuckles mountain range, a world heritage conservation area, is one of Sri Lanka's major nature attractions.
The reserve attracts hundreds of local and foreign tourists for trekking and witnessing its waterfalls.
The Knuckles range consists of rugged mountain peaks interspersed with streams and cascading waterfalls. It covers an area of 18,512 hectares.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
