Messick, 50, who was battling from depression for years and was recently diagnosed with bipolar disorder, committed suicide in Los Angeles, her family had said in a statement.
McGowan paid her tributes to Messick on Instagram and without naming disgraced movie mogul Harvey Weinstein, blamed him, for causing "so much damage".
"For Jill: May your family find some measure of solace during this pain. That one man could cause so much damage is astounding, but tragically true.
"The bad man did this to us both. May you find peace on the astral plane. May you find serenity with the stars," she wrote alongside a photo of the sun behind the earth viewed from space.
Also Read
In the aftermath of multiple exposes that revealed the extent of Weinstein's sexual transgressions, McGowan went public with her own account.
She had claimed that ex-manager arranged the meeting with Weinstein, which took place in a hotel room.
Messick was named as a part of an email exchange released by Weinstein, where his attorney Ben Brafman showed a message from her to reveal how she allegedly defended his client.
Disclaimer: No Business Standard Journalist was involved in creation of this content