"[He was] screaming and crying [that] he'd been bashed at the local park. I just took off and raced over."
The group attacked the boy from behind while he was running in Spargo Reserve in Massey.
Now the single mother of four is warning other parents in the area to look out for their children.
"It could've been anyone's child. When I drive out my driveway, I look at the high school kids and think they are walking home innocently, are they just going to pick one of them up on the side of the road and do it to them?"
She said she'd never heard of anything like this happening in her 46 years living in the area.
"I'm fuming. He's a good kid," she said.
"It was just a random attack. He goes to a good school. They're obviously just [travelling] around attacking youths for no reason."
Williams is thinking of packing up her life in Auckland and moving out of town.
"I spoke to my mate in Christchurch. I'm thinking of just packing my kids up and going. There is nothing here. They are not safe."
The teenage victim says the attack came "out of the blue".
"I just felt shocked and in pain, really," he said.
"I didn't know them, didn't see them."
He said the attack lasted between three and five minutes.
He didn't see any of his attackers, but he could hear that a woman was trying to help him.
The woman left after she felt unsafe, he said.
He spent a night recovering in Middlemore Hospital, where he got more than 40 stitches to his upper lip and mouth.
Williams said she could still see the attackers' shoe prints from where they had stomped on her boy's hands.
She's now appealing for information and for any witnesses – including the woman who tried to help her boy.
"I would like to thank the lady for at least trying to help. I would love to find her. She would have a description. She was scared, so she took off, which is totally understandable. Four against one is not a good thing."
Police would also like to speak to the woman and urge any other witnesses to contact them on 105, quoting file number 201023/8330.
Waitematā Police Acting Senior Sergeant Greg Wilson said inquiries into the case were ongoing.
"We want to reassure the victim, and the community, that we are doing all we can to locate the offenders," he said.
"We believe there are people who witnessed what happened and may have vital information that can help us identify and locate the offenders."
Williams said she will go door knocking to find any more potential witnesses.
