The 41-year-old actor-maker and his childhood friend Matt Damon co-wrote the script for the 1997 drama, in which they also starred.
"Heartbroken. Thanks chief - for your friendship and for what you gave the world. Robin had a ton of love in him. He personally did so much for so many people. He made Matt and my dreams come true.
"What do you owe a guy who does that? Everything. May you find peace my friend," Affleck wrote on his Facebook page.
Robin Williams died of an apparent suicide on August 11.