The parents of a 15-year-old London girl who mysteriously disappeared from a Malaysian resort a week ago said on Saturday that she wasn't independent and had difficulty walking, in new details to support their conviction that she was abducted.

A massive search operation has been underway for Nora Anne Quoirin, who was discovered missing by her family last Sunday morning from the Dusun eco-resort in southern Negeri Sembilan state.

Police believe the teen climbed out through a window in the living room that was left open and was still in the vicinity of the resort. They are treating her as a missing person but do not rule out a possible criminal element in her disappearance.

But her parents, Irish Meabh Quoirin and her French husband Sebastien, said that Nora Anne was born with holoprosencephaly, a malformation that causes her to have a smaller brain and led to learning and physical disabilities.

"All her life she has spent a lot of time in hospital. When she was born, she needed operations to help her (breathe). She has specialists that monitor her growth, her physical abilities and her strength, and especially her mental capacity," they said in a statement released by the Lucie Blackman Trust, a British charity that supports people involved in crises overseas.