A Melbourne mother says a "good Samaritan" whose ute was stolen when he stopped to help her son on a busy Melbourne road has saved her child's life.

Jennifer said she was "frantic" when her 14-year-old son Darcy, who has autism, "escaped" from the family's home last night.

She said there was no question in her mind that the actions of several people who stopped to help saved her son's life.

"He was in the middle of the road, weaving in traffic, cars traveling at speed, I just can't imagine how he wouldn't have been hit," she said.

Jennifer said her son is the size of an adult but has no road sense or awareness of danger.

"Darcy was in such a dire predicament, a life-or-death situation," she said.

"He is lovely, bubbly, he's affectionate but he's like a little puppy — completely carefree and oblivious to any of the dangers of the world."

She said the three men who stopped to help her son need to be celebrated.

"Darcy doesn't have any road sense whatsoever and we're just indebted to those guys," she said.

'Good Samaritans'

Aaron says he doesn't care about his stolen car and would do it all again to help the boy. ( ABC News )

One man, whose new ute was stolen when he stopped to help Darcy, said last night's incident had shown the "absolute best and the absolute worst of people".

Aaron, who does not want his last name published, said he was concerned when he saw Darcy on the road at Maidstone in Melbourne's west.

"I'm on my way home last night, I was coming up Rosamond Road and I noticed a young lad running into oncoming traffic on the other side of the road," the 39-year-old said.

"Obviously it concerned me, so I slowed down and flashed my lights and I wound my window down and tried to communicate with him and he wasn't really giving me anything.

"He was running a little bit erratically, he was on the road, off the road, on the footpath, the nature strip, then he was smack-bang in the middle of the road, running full tilt.

"Cars were slamming on the brakes. I thought he was going to die, I thought he was going to get hit by a car."

Aaron jumped out of his car and said he and another motorist helped "hustle" the boy off the road and care for him until police arrived.

"Initially I thought maybe he might have been deaf, because he wasn't really communicating," Aaron said.

"I was just saying 'hey mate, do you want to come off to the side of the road, do you want just hold my hand for a minute, do you want to just walk with me for a minute?'.

"I was just trying to calm him down because he seemed a bit worked up."

'The best and worst of people'

Aaron said the child ignored him and seemed agitated, but wasn't crying.

He then discovered that his car that he bought just before Christmas had been stolen.

"I can't remember, it all happened so quick," he said.

Aaron bought the ute just before Christmas. ( Supplied: Victoria Police )

"I quite literally just pulled the car up on the side of the road and jumped out. I know the window was open, I don't know whether I'd switched the car off or if I'd just left it in park.

"It's just a car, it is a new car and I love it. But it's just a car and that's what you pay insurance for.

"The car doesn't even mean anything to me … but what was more important for me was that this kid didn't get hit by a car, so I would absolutely do it again."

As well has having his car and laptop computer stolen, Aaron says the thieves spent about $2,000 on his credit card.

He said situations like this bring out the "absolute best and the absolute worst of people".

"You've got people there trying to do the right thing and putting themselves on the line for other people, including the police officers, and then you've got the bad eggs who want to come along and take advantage," he said.

Pair arrested, ute still missing

Police praised Aaron, saying he risked his own life to help the child.

"It could have been a very different set of circumstances had he not intervened," Detective Senior Constable Tony Schearer said.

"He should be commended for the actions that he took — he put his own life at risk going through the oncoming traffic,"

Police arrested a 52-year-old West Melbourne man and a 41-year-old Maidstone man in an allegedly stolen car earlier today.

They have not yet found Aaron's stolen car.

Both men are assisting police with their enquiries, police said.

Police are asking anyone who sees the black 2017 Ford Ranger ute with registration plates ARP-988 to contact them.