Judith Ansell has flown to Melbourne to help with the search for her son Jonathan and has appealed for anyone who knows where he has gone to come forward.
The 27-year-old, from Jordanhill, Glasgow, had been travelling Down Under for more than a year, but dropped out of contact with his family around Christmas time.
Then Mr Ansell suddenly got in contact on April 23 to say that he had lost his passport and run out of money and was living on the streets, before the line went dead.
Mrs Ansell said: "I said 'Jonathan, thank God it's you. Where are you?'. He said he was in Melbourne, and I said 'what's wrong, what's happened?'.
"He said he had run out of money and was living rough."
She described him as quietly spoken and has told police officers she believes he may not approach people for help if he was in trouble. He was officially reported as missing on Monday.
Mrs Ansell added: "I said he should go to the police and not be embarrassed and that everybody loves him."
The missing man's cousin Kirsten Ferguson made an appeal for help on Australian television yesterday alongside his mother, and said that the situation had come out of the blue.
Miss Ferguson was also travelling in the region but has put her holiday plans on hold while she helps search for her relative. She said: "This sort of situation, you never think your family will be in. We all just want him home and for this nightmare to end."
The family have turned to social media and have circulated Mr Ansell's picture on Facebook and Twitter, along with a brief description and information on his last known whereabouts.
They have created the symbol - #findjonathan - on the micro-blogging site to make it easier for people to provide information or make appeals in a single place.
Hotels and guest houses in Australia have been posting or retweeting Mr Ansell's details.
Police have launched an investigation and have appealed for anyone who may have seen Jonathan to contact them. It is known he was recently staying at the St Kilda guesthouse near Melbourne, but moved out last month.
It is thought that he may have grown a beard. Officers are worried about his mental state and have stressed he is alone in an unfamiliar city thousands of miles from home. They say he may still be in Victoria State, but say it is also possible he has now left the area.
Acting Inspector Dale Huntington, of Victoria Police said: "He was in a distressed state and I told his family he was without a passport and without money. He was in a very, very sad state."
He is of Caucasian appearance, 5ft 9inches tall, with a fair complexion and short, light brown or dark blonde hair.
A Foreign Office spokeswoman said: "We are liaising with the local police. We are providing consular assistance to the family."