Juarez was a freshman on the junior-varsity football team and a star athlete at Hollywood High.
An autopsy will be conducted to determine the exact cause of death.
Grief counselors were on hand on Monday at Hollywood High School; Joseph Le Conte Middle School, where Juarez formerly attended; and West Adams Preparatory High School, where Friday night's game was held.
"I miss him, I really do miss him a lot. Just a very humble person," said Bryan Moran, a friend of the victim.
Hollywood High School took a moment of silence in honor of the teen.
"The students are trying to make sense of, you know, how can someone so young, who's so close to their age, also pass away," said Holly Diaz, an intervention expert at the school.
There were two minutes left in the game Friday night when Juarez collapsed on the field. Teammates said Juarez had just taken a hit, and as he was jogging back to the sidelines, he fell over.
"He was on the floor, and everybody started to panic because he was just laying there, he didn't get up," said student Rigoberto De Leon.
Officials immediately stopped the game, and Juarez was rushed to Childrens Hospital Los Angeles.
Friends and family gathered by his bed all night. Juarez was pronounced dead on Saturday afternoon.
"He was very special. Like, you wanted to see what was going to happen with his life because you knew he was going to go places," said teacher Bonne Anderson.
Juarez also played baseball and ran marathons.
Juarez's coach said he was a dedicated athlete who also did well in school.
Friends are planning to hold a memorial to honor the JV football player.
He is the second high-school football player to collapse during a game in about a month.
Garden Grove High School student Kevin Telles, 17, died just last month. The cause of his death is still under investigation.