Daniel Pollock - He was co-star in Romper Stomper with Russell Crowe in 1992. A few months after the movies release, he jumped infront of a train. He was just 23 years old. He was a heroin addict, and was battling depression, as well as a real life break up with Romper Stomper star Jacqueline McKenzie (Deep Blue Sea, etc.). Very tragic.
Corey Haim - Childhood star who acted in the Lost Boys, Silver Bullett, License to Drive, etc. got lost into the world of drugs, through childhood trauma from being a child actor, and sadly passed away at the young age of 38 years old in 2010.
Justin Pierce - Star of Next Friday and Kids tragically hanged himself at age 25. He was a keen skateboarder, but unfortunately was also a heroin addict. A break up with a girlfriend spiraled him into deep depression.
To a lesser extent - Corey Feldman and Macaulay Culkin.