In a police statement, Tupou was described as "a fun-loving, hard-working young man who regularly attended church and enjoyed social occasions with his friends and family".
"At this stage we believe the offender was not known to him," said Detective Senior Sergeant Darrell Harpur.
"We are committed to locating the offender or offenders and holding them to account.
"We are appealing for anyone who witnessed this incident, or anyone who has any information at all that may help us with our investigation, to come forward and speak with police."
Tributes have been flooding social media after news of his death.
A relative, believed to be his sister, wrote of her heartbreak in already losing one sibling and now losing her beloved brother.
"For the longest time it was just us two. Then Ma'afu came along and it was us three. But then he broke our hearts when he left us and you promised it was gonna be us two to the end ... but my heart's breaking again cause now it's just me.
"Two biggest heartbreaks of my life and they're both from you and Ma'afu. Can't bare another one so watch over mum and dad and the fams. You said you got me, so make sure I don't have another broken heart anytime soon okay?"
A friend wrote "Ofa atu to my toko for life! Samu ofa atu toko ... we out here in the 104 hurting bro! Fly high with Ma'afu!", while another relative wrote "I miss you toko".
Harpur said police wanted to speak to anyone who may have sighted a light or gold-coloured people mover, similar to a Honda Odyssey, in the South Auckland area on Friday night or early Saturday morning between 2am and 6am.
If you can help, please contact Counties Manukau Police on (09) 261 1300 or provide information anonymously through Crimestoppers on 0800 555 111.