The tragic incident has left the actor grief-stricken, his publicist said.
Authorities were investigating the cause of death, but details were not immediately available.
Paramedics were called, but he was pronounced dead at the scene.
“Sylvester Stallone is devastated and grief-stricken over the sudden loss of his son. His compassion and thoughts are with Sage’s mother, Sasha,” News.com.au quoted publicist Michelle Bega as saying in a statement
Los Angeles police said they were dispatched to investigate a death at a home on Mulholland Terrace around 2:15pm but could not confirm the person’s identity or offer details.
Coroner’s officials also said they were in the initial investigative stages.
“Sage was a very talented and wonderful young man, his loss will be felt forever,” Bega said.
George Braunstein, an attorney who has represented Sage for 15 years, said a housekeeper found his body Friday afternoon.
Friends and acquaintances had become concerned because they hadn’t heard from Stallone in the past day, Braunstein said.
Sage Moonblood Stallone was the oldest of the ‘Rocky’ star’s children and co-starred with his father in two films. He was the first of two sons Stallone had with first wife Sasha Czack.
Sage made his acting debut in 1990’s ‘Rocky V’ and also appeared with his father in 1996’s ‘Daylight.’
Also in 1996, Sage Stallone and veteran film editor Bob Murawski co-founded Grindhouse Releasing, a company dedicated to preserving and promoting the B-movies and exploitation films of the 1970s and 80s.
“He was very respectful of all the actors in all the movies,” Braunstein said.
“You couldn’t mention a movie that he didn’t know everything about.”
Sage also directed the 2006 short ‘Vic,’ which screened at the Palm Springs Film Festival.
Braunstein said Stallone was planning on getting married for the first time, and had frequent requests to work on films.
“He was a full of life filmmaker with his whole future ahead of him,” Braunstein said. “He was just very up and enthusiastic and positive.
“I think it was probably some sort of accident,” he said of the death.
Braunstein said Sage greatly admired his father but was working hard to make his own name in the film industry.
“He was very proud of his father and proud to be his father’s son,” Braustein added.