The 41-year-old, who played Richard 'Boner' Stabone' in the sitcom, was discovered dead at a Vancouver park yesterday after being reported missing last week.
Speaking to Us Weekly, Gold - Carol Seaver on the show - said: "Today is a sad day. My heart is broken for Andrew's family."
She added: "I have such great memories of Andrew and our time together on Growing Pains."
Co-star Kirk Cameron has also paid tribute to Koenig, saying that his "prayers" are with the actor's family and asking for people to respect their privacy.
Koenig's family previously thanked the public for their support following his disappearance, and revealed that they were planning to bind the letters they have received into a "rememberance book".