Fanie was one of the 10 victims of the gruesome attack that took place in Sizzler's gay massage parlour in Sea Point early on Monday morning. Eight of the 10 men died.
The victims' hands were tied with duct tape before they were shot in the back of the head and had their throat slit. Eight died and two are still in hospital, one of them in a critical condition.
His distraught mother, Anita Fouché, said she had spoken to her son on Sunday, a day before the massacre. He visited them two weeks ago, and there was no mention of problems at work.
Fanie finished grade 10 at Theunissen High School before moving to Cape Town, where he got a job.
High school principal Fanie Beukes said Fanie was a quiet boy who never caused trouble. "He was a nice kid."
Abe Bush, who worked at Sizzlers for three months last year, said Fanie worked under the pseudonym Ryan.
He and Fanie were friends, he said.
"The advertisement said he was older, but he told me he was only 17."
When handing a school photograph to Die Volksblad newspaper, a tearful Mrs Fouché said: "Please return the photograph, it's all I have left."
She said her husband, Nefie, had already left for Cape Town.
"We don't want to talk about Marius. Police said we must say nothing.
"People can say and think what they want. We knew him and he was a good person."