"Mani will be remembered as a beautiful, smart, witty young man who lived life to the full," Armstrong said.
"Mani was a product of amazing parents. Our small, tight community are wrapping our arms around our young people to help them through this time in their young lives."
Local surfers on Saturday night said they believed the shark was a great white that attacked from below and bit one of Mani's legs.
The shark struck a second time, mauling the other leg and tearing a fin off the board.
Nearby surfers tried to stop the bleeding in the water before getting him to shore.
They performed first aid until the ambulance arrived.
Jake Trevillian, who has a daughter Mani's age, described Mani as an individual who followed his own path.
"He grew up here. All the kids out here are pretty tight," Trevillian said.
"The world was his oyster. You could say that about a lot of kids, but he was really clever, artistic, not shy, and they all loved him.
"He loved making his own surfboard, not many other kids are like that. He was an individual and didn't follow the path of everyone else, and one of those ones you could tell he was going to do something cool with his life."
Police took away Mani's logo-less surfboard, which featured deep bite marks across the right tail, suggesting the teenager was laying, or paddling on his board when attacked.
The bite marks will be used by state government shark experts to determine the species of shark responsible. Great white sharks follow the whale migration north along the coast at this time of year.
Surfing along the Yuraygir Coast is the No.1 pastime of the small seaside village of Minnie Water and Mani was in the water as often as anyone, Trevillian said.
"He loved being in the ocean," he said.
"He was constantly surfing in the water. There's a crew that surf more than anyone at the moment and he's part of that."
Friend Kyra Geerin posted a heartfelt tribute on Mani's latest social media post.
"Hope heaven is good to you," Kyra wrote.
"We will miss you more than you'll ever know."
Trevillian said this was the first shark attack he was aware of at the nearby beaches.
The youngest NSW victim was Ken Murray, 13, who died while free-diving below Roseville Bridge in 1960.
Wooli resident Helen Dobra rushed to the beach to see the boy's family and paramedics crowded around his body.
"It was a really traumatic scene, my heart's still pumping, it's going to be a real shock to our community," Dobra said.
"We have a very, very close community here in Minnie Water, so it's quite tragic.
"Everyone knows the family, we're all really close. It will hit the community really hard."
Beaches in the area, including Wooli, Diggers Camp and Minnie Water, have been closed.
"Officers from Coffs/Clarence Police District will be liaising with the Department of Primary Industry to investigate the circumstances surrounding the death. A report will be prepared for the Coroner," NSW Police said in a statement.
Great white sharks are following the whale migration north along the NSW coast at this time of the year.
