"Heartbroken to continue to watch sweet, kind souls be consumed by darkness," tweeted Williams, whose father died of a suicide in August 2014. "May it never hurt less, so we never grow numb to the loss."
Williams also shared a link for Pieta House, a suicide prevention treatment center in Ireland. Zelda shared the link "in honor" of White, who hailed from Tipperary, Ireland.
White had favorited a message Williams shared on Twitter the day her dad died, which was a quote from the classic book "The Little Prince" by Antoine De Saint-Exupery.
White, who had been in an on-and-off relationship with comedian Jim Carrey, was found dead at her home in Sherman Oaks, California on Monday night. Her death is being investigated as a suicide.