The five men were believed to be heading to the Auckland Darts Masters competition on August 12.
Police described the incident as a "completely unprovoked attack".
The mother of one of the teens said her daughter and male friend were travelling home on the train when they were confronted by five drunk men wearing Four Square costumes and masks.
"The kids were on the train near them and one of the men started walking around and telling my daughter to put her hand in his pouch, because he was wearing an apron.
""He then got his d*** out and exposed himself to her," she said.
"Then one of the other guys suddenly took a disliking to the boy she was with. He called him a f*****, rolled up his sleeves and started choking him."
Police said last week that two men had come forward after media coverage of the incident, including video footage.