Koenig's body was found Thursday in Stanley Park in Vancouver, British Columbia. His family had alerted police because they had not heard from him in more than a week and were worried because he suffered from depression.
The former "Growing Pains" actor's father, Walter Koenig, told reporters Thursday his son had taken his own life, but did not disclose the cause of his death at the age of 41.
"Today is a sad day," Tracey Gold told UsMagazine.com in a statement Thursday. "My heart is broken for Andrew's family. I have such great memories of Andrew and our time together on 'Growing Pains.'"
E! News said Milano, Shatner, Sarah Silverman, Wil Wheaton and Candace Cameron took to Twitter to offer their condolences.
"My heart is heavy for the Koenig family," said Silverman, while Milano Tweeted, "RIP."
Shatner, who worked with Walter Koenig on "Star Trek," wrote: "My deepest sympathies to Andrew Koenig's family. I will grieve with them."
Wheaton, a former cast member of "Star Trek: The Next Generation," posted on his Twitter page a message that said: "Oh my god. I just heard that Andrew Koenig's body has been found in Vancouver. He was only 41. My heart goes out to his family."
"Heartbreaking. Our prayers go out 2 his family," said Cameron, the sister of Koenig's "Growing Pains" co-star Kirk Cameron.
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