Rosillo moved to New Zealand from the Philippines at age 13. He started high school on the North Shore before his family moved to Pakuranga three years ago.
The former Edgewater College student was nicknamed "WOF" because he was so keen on cars.
Close friend Marissa Daniels said: "He was the Warren of Fitness. You wouldn't go and buy a car or do anything to your car without Warren there."
The two had dated in high school and remained good friends. Marissa's family had taken Rosillo in when his relationship with his parents became strained.
Friend Eiken Elazegui said Rosillo had begun to patch up his relationship with his parents. Elazegui said he visited Rosillo's parents yesterday, who were in shock.
"It's really hard for them. They don't believe it," Elazegui said.
"He hadn't talked to his parents for a year [then] a month ago they started talking again."
- with NZPA