Leo Nicholson, 19, from Thornley, Durham, was detained in the Southeast Asian country on Thursday, April 30.
The teen was reportedly found with a quantity of cannabis in his shared apartment – an offence in that country that could see him jailed for decades or put to death.
The family say they believe as Leo is a vulnerable adult with autism that they believe he was coerced into the situation.
The Foreign Office has confirmed that a British male has been detained in Malaysia, and that they remain in contact with the local authorities.
Leo’s family say they have limited access to their son and little information around the circumstances of his arrest.
His dad, Arron Nicholson, 41, said: “It is unthinkable he is looking at 30 years minimum for all we know but he could be facing the death penalty as the laws are so different over there.”
The family say they believe Leo may have been pressured or influenced by others he was with.
They say Leo told his dad days before his arrest that he was making plans to return home.
Arron said: “I have gone from expecting to see my son in a couple of days to now not knowing when I will next see him, we are just desperate now and praying for him.”
Arron, a former soldier, believes Leo was in trouble and forced to make the trip from the UK to Asia the day before his birthday on April 7.
He has been in the country for around three-and-a-half-weeks.
His loved ones are now trying to raise around £50,000 for an experienced defence lawyer in Malaysia and to cover their travel costs to fly over to the country.
A fundraiser has already raised more than £3,600 in under 24 hours, at the time of writing.
The gofundme states: “We urgently need to raise funds for:
“An experienced defence lawyer in Malaysia
“Legal and case-related costs
“Travel expenses, so we can support him through this process.”
The British Embassy has been in contact with the family and is working with them as the case develops.
A Foreign, Commonwealth and Development Office (FCDO) spokesperson said: “We are supporting a British man who has been detained in Malaysia and are in contact with the local authorities.”