"I don't believe he's dead,'' she said of her son.
"I believe that someone saw him. He cannot just disappear like this.
"I know that someone knows what's happening with my son. And they have to speak out. We need our son back."
A police-led search of the Rangitata River near the family's Temuka home proved fruitless today.
There was no sign of Yuri, so police called off physical searches for him.
They were instead focusing on pursuing leads from the public.
Santana said an ex-classmate of Yuri's from Geraldine High School had contacted police about a possible sighting. However, the girl was not certain it was him.
Santana hoped more people would speak out with information about where her "very funny, very friendly, popular" boy was.
"We need help. All we can do we are doing everyday. We need clues."
It was hard for her and her husband to be in their house because they were constantly reminded their son was missing, Santana said.
They weren't living, she told the Herald, merely "surviving" and trying to stay strong for their 7-year-old daughter, Yuri's sister.
Santana said her son spent the day before he went missing playing basketball and swimming - two of his favourite past times.
Officer in charge, Sergeant Mike van der Heyden of Temuka, told Fairfax Yuri may have hitch-hiked out of the Temuka area.
Police believed the teenager did not want to be found, he said.
A police spokeswoman told the Herald tonight they were still actively searching for the teen and continue to appeal to the public for any information or sightings of him.
"Police have received numerous reports of sightings of Yuri and are following up on these,'' she said.
"They are also following up with known associates.''
Have you seen Yuri? Anyone with information on his whereabouts is urged to contact police on 111 or Crimestoppers anonymous on: 0800 555 111.
