A police officer pastes a photo of 15-year-old Irish girl Nora Anne Quoirin who went missing from a resort on a wall at a shop in Seremban August 9, 2019.
President of Ireland, Michael D Higgins, said: "Sabina and I offer our deepest condolences to Nora's parents, Meabh and Sebastien, to Nora's siblings and to her extended family".
The Lucie Blackman Trust, a charity supporting missing people overseas, said police believed the teenager could have been taken.
Investigations are underway to identify the body and establish the cause of death. Get it for your iPhone here.
Mohamad Mat Yusop, Negeri Sembilan state police chief, told reporters that "the body of a white female" was found just before 2:00 pm (0600 GMT) after authorities received a report from a member of the public.
The Lucie Blackman Trust, which is handling media enquiries for the family, says that it can not confirm that it is Nóra but that it is likely.
National Malaysian newspaper the Malay Mail has reported that a body had been found in the search for Nóra.
Ms Quoirin explained to the press on Monday, Nora was their first child.
Search crews looking for Nora had played her mother's voice in the dense Malaysian forest near where she disappeared.
LBT said that an update would be given "as soon as possible" and asked for the family to be given privacy.
An anonymous donation from a business in Northern Ireland - Nora's mother is from Belfast, and Nora was traveling on an Irish passport, according to the BBC - helped the Quoirins offer about $12,000 for information that could lead them to their daughter.
Meabh Quoirin said: "Nora is so precious to us and our hearts are breaking".
She has severe learning difficulties and needs help with many everyday tasks.
Police leading the investigation have refused to rule out a "criminal element" in the teenager's disappearance.
St Bede's School in south London, which Nora attended, has opened its doors to allow the community "to join in prayer for Nora and her family.in this heartbreaking and horrific moment".