The Garfield High School senior has been participating in the club after school for more than 10 years.
As an alternative to living life on the streets or joining gangs, Leos calls the club a safe place where he learned how to make friends.
"If you needed someone to talk about, like problems at home, they were there for us and that's what I ended up becoming for the kids here as well," the 19-year-old said.
Now he hopes to return his positive experience to those just joining.
"I love helping people out because I realized how much people have helped me out and helped me get to where I want to be," Leos said. "It's important to give back."
Leos' packed schedule also includes football, track, swimming, honors classes in school and hosting blood drives.
Recently, he traveled to the Dominican Republic to help families in need.
"His development and his maturity and the amount of giving back that he does is quite impressive," said Anna Araujo, executive director of the East L.A. Boys & Girls Club.
Currently, Leos is deciding which California university to attend in the fall, where he will study political science as part of his mission to continue to make a difference.
"Through policy (we can) help make it easier so that we can provide resources to kids who are in disadvantaged communities like this one, where I come from," Leos said.