Nora Quoirin, 15, from London, disappeared from the Dusun Resort in the town of Seremban, about 60km south of Kuala Lumpur, with her parents finding her room empty on Sunday morning (local time).
Police are using sniffer dogs to search for 15-year-old Nora Quoirin, who has learning difficulties.
"We are appealing to everyone to assist the local police in any way they can and to pass on any information that would help locate our beloved Nora without delay".
Quoirin's aunt Aisling Agnew said as a child born with special needs and learning and development disabilities, it makes Quoirin especially vulnerable.
It's unclear how or why Nora came to leave her hotel room.
This article, British teen goes missing from Malaysian resort while on family holiday, originally appeared on Coconuts, Asia's leading alternative media company.
Police have deployed an additional 40 personnel from the Police General Operations Force from Cheras as the search for an Irish girl who went missing yesterday intensified, bringing the number of those involved in the search to 159.
The Dusun Resort is secluded accomodation about an hour from Kuala Lumpur.
"She is 15 with special needs, and hasn't been seen since everyone went to bed last night".
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LBT's chief executive Matthew Searle said: 'This is a very vulnerable young girl missing in a remote location.
Nora arrived in the country with her mother, father and two siblings on Saturday for a two-week trip.
But on Sunday her parents awoke to find she was missing.
Police are treating the disappearance of a girl traveling in Malaysia on an Irish passport as an abduction.
"They had just arrived - it was going to be a trip of a lifetime", family friend Catherine Cook told the BBC.
CNN has contacted the Irish Department of Foreign Affairs and the Malaysian Embassy in London for comment.
Ms. Agnew added: "We now consider this a criminal matter".
"All officials are still up there at the hotel, we discussed with them all, and God willing, we will continue the search until it is successful", he said.
"We are continuing with the search and we have also informed all district police chiefs to help out", she said.