IN JAIL: Quentin Samson was arrested after allegedly taking a taxi driver's phone.

A New Zealand teenager's drunken night out in Thailand has ended on the cold concrete floor of a Bangkok prison.

Quentin Samson took a holiday to Thailand to celebrate his 18th birthday but soon found himself behind bars, charged with theft in the night.

His brother-in-law, John Burns, speaking from Auckland said five days ago Samson went out to celebrate the 21st birthday of his friend, Ashton Holmes. They had had a few drinks when Samson disappeared without notifying anyone.

He caught a taxi back to his hotel and, in his intoxicated state, allegedly stole the taxi driver's phone.

Police arrived and Samson gave the phone back but resisted arrest, afraid Holmes would not be able to find him if he was in jail.

Holmes spent the next 48 hours frantically searching hospitals for Samson before being notified of his arrest.

Police had taken him into custody and charged him with theft in the night, which carries a stiffer sentence than theft during the day, Burns said.

"Apparently that's a worse charge if you do it at night-time rather than the day, it's a very serious crime."

If the theft had occurred during the day the maximum penalty, if found guilty, would be up to three years' imprisonment.

For theft in the night it was one to five years' imprisonment.

Bail was about 60,000 (NZ$2250), which neither Samson or Holmes were able to pay, Burns said.

"With no money and no-one over there it is a hard thing to deal with, especially for a young guy," Burns said.

Since the arrest Samson had been transferred from the police cells to a Bangkok prison.

It would be a living nightmare for him in there, Burns said.

"I couldn't imagine what it would be like.

"I've watched a few things about people in Thai prisons and no-one is ever certain of when they are going to get out."

Holmes' mother, Tracy, said in an email to family that Holmes had taken Samson a blanket as he was sitting on a cold, concrete floor in prison.

Samson was a good kid who made a drunken mistake and did not deserve such harsh treatment, she said.

The family were rallying together to raise the money needed to make bail.

A Ministry of Foreign Affairs and Trade (MFAT) spokesperson said MFAT was aware of the arrest and providing consular support.

Staff from the New Zealand Embassy have sought approval to visit Samson on February 5, the spokesperson said.

"The Embassy's role is to monitor Quentin's welfare and ensure that he has the same rights as other detainees in Thailand.

"Consular staff are providing updates and advice to Quentin's family."

MFAT could not comment on the investigation or interfere in the judicial proceedings of another country, the spokesperson said.

Originally from Auckland, Samson moved with his family to Australia in September and had been working hard in a new job, which helped him pay for the trip, Burns said.