Depp, 54, Sheen, 51, and Dillon, 51, came together at Depp's house Sunday more than 30 years after the Oliver Stone movie opened in theaters in December 1986.
"#platoon 30 year #reunion last night at #johnnydepp house #goodtimes @charliesheen," Dillon captioned a photo on Instagram of himself with Depp and Sheen.
Platoon starred Sheen as Private First Class Chris Taylor, with Depp as Lerner and Dillon as Bunny. The anti-war film was set during the Vietnam War, and co-starred Tom Berenger, Willem Dafoe and John C. McGinley.
"I think a big reason we're all still friends is because we all had such an exceptional experience shooting that movie," Dillon told the Daily Mail in December.
"It was just such an incredible experience," he added. "I still look back on it as such a great time in my life. I was young and I loved it."
Platoon won four Oscars, including Best Picture and Best Director for Stone. Stone confirmed in an interview with Entertainment Weekly in 2011 that he hired Sheen after considering Depp, Keanu Reeves and Kyle MacLachlan for Taylor.
"Charlie was a dumb-struck 17-year-old the first time he came in for the film, back when we were going to make it '84. And in those two years, he'd grown and seemed perfectly wide-eyed and had a vaguely privileged look," the director recalled.
"I think he did a great job," he added. "He was perfect for the movie. He conveys the horror of the place. I like his performance."
Depp, Sheen and Dillon have since starred in the Pirates of the Caribbean movies, Two and a Half Men and Entourage, respectively.