Gary Pearce's family says his life might have gone a little off course, but he was still a "mummy's boy" and his disappearance is almost impossible to understand.

The 21-year-old from Albion Park, south of Sydney, was reported missing five weeks ago by his family, who is now offering a $10,000 reward for information that might lead to his return.

Gary Pearce was last seen in North Wollongong on Tuesday April 23.

The last time his mother, Joanne Pearce, spoke to him was on the Sunday before he disappeared.

"He rang me, he was hysterical. He had a fight with some fellow at Port Kembla and his phone cut out," she said.

Mrs Pearce said she then contacted police, and they came back to her saying he was fine, he had been in an altercation, but he would sleep it off.

"But he kept messaging me, he said he was 'shitting' himself and I could tell by his messaging that he was either high or drunk, and I told him I'd contacted police, and he would be fine," she said.

The next day Gary Pearce tried to call his mother, but she missed the call, and that was the last time he attempted to contact her.

The past five weeks have been tortuous for the family as they try to find information about what has happened to their youngest son. They have created a Facebook page and hashtag #keepthelightbrightforgary.

Joanne and Gary Pearce are offering $10,000 for information on their son's disappearance. ( ABC Illawarra: Kelly Fuller )

Mrs Pearce said her son was a kind-hearted person.

"He was a bubbly sort of person, who had a lot of challenges in life, which he tried to overcome. He made me laugh all the time, he was a bit of smart arse, but he was my baby," she said.

"He loves his mum, would talk to me every day, loves his brothers and his sister, and unfortunately he has a niece now that he has never seen.

"He loves mechanics and cars and trucks and his goal in life was to always be a truck driver like his dad, but unfortunately, he liked to drive very fast, so he kept losing his licence."

Mrs Pearce said her son had odd jobs, but found it hard to hold down work, she believed because of his Asperger's.

"He went out to the bush to a property in the middle of nowhere near Alice Springs and he loved it, herding cattle, fixing fences, and the only downside was it was so far from home and he couldn't call me every day, and he struggled with that," she said.

His father, Gary Pearce, said over the past couple of years his relationship with his son had become complicated because he knew he was involved with drugs.

Gary Pearce's family says he loved being on farms and enjoyed his time working as a jackaroo. ( Supplied: Pearce family )

"He knew my standing on drugs, so does the rest of the family, so we probably had a bit of a strained relationship, but he also knew I was there if he needed me, at any time.

"He was a good kid, at the end of day he was good kid."

Mrs Pearce acknowledges her son had been in trouble, even serving six weeks in jail for stealing petrol, but they said he had surrounded himself with people who preyed on his naivety.

"We know how he was led into drugs," she said.

Mr Pearce's heartache has been increased because the last time he spoke to his son, Gary told him he needed a new place to live and asked to borrow his caravan.

Gary Pearce dancing with his mother at her 40th birthday party seven years ago. ( Supplied: Pearce family )

"He was running out of places to live and I have an off-road camper, and he asked could he use it and I told him we were using it on the weekend, and he hung up on me, and was the last I heard of him."

Both parents now fear their son is dead.

"My gut reaction was he ran into foul play, straight off the bat, because everyone was talking suicide, but I said no," Mr Pearce said.

"My reaction was someone has caught up with him, someone has taken him."

Mrs Pearce said she knew he was mixed up with the wrong people.

"I figured when they had been on a drug high or something, he has irritated some people and something has got out of hand. There are many theories that go through your mind.

A poster created by Gary Pearce's family offering a $10,000 reward for his return. ( ABC Illawarra: Kelly Fuller )

"But I just think that somehow someone that he was involved with has got really annoyed with him and done something to him, whether it was intentional I don't know," she said.

Out of desperation, the family has now gathered together $10,000 as a reward for his return.

Mrs Pearce said a friend had offered them the money.

"We were fortunate to get that money and originally we were going to use it for a private detective, but we've done some research and we feel that the reward is the best option, and mostly because we are desperate.

"We hope it will motivate someone to tell us, just tell us where he is."

Mrs Pearce said the situation had destroyed their world.

"This is now my one job; all we want is to know where he is to bring him home. Either way, he doesn't deserve to be out there like a piece of garbage."

NSW Police said the investigation into Gary Pearce's disappearance was continuing.