Moore's Twitter account, mrskutcher, was among those responding to a message from a young man threatening to hang himself in Casselberry, north of Orlando. Moore - with more than 2.5 million followers - and husband Ashton Kutcher are both active on the social network.
Vardalos' eponymous account included a message that she had called a suicide hotline and been connected to Florida police. "I gave his name+city. They went to home, helped him," one message read.
The Seminole County Sheriff's Office said authorities received two calls around 2:30 a.m., one from California and one from Vancouver, British Columbia. Both callers reported the suicide threat on Twitter. There was no record of the callers' names, Lt. Sonia Pisano said.
Deputies went to a home and took an uninjured juvenile male to a hospital, Pisano said. She said she could not provide more specifics.
Calls to representatives for Moore and for Vardalos, who starred in "My Big Fat Greek Wedding," went unanswered early Friday.
Moore's Twitter account was involved in a similar case last April, when a California woman messaged that she was going to kill herself. San Jose police said they took a woman to a hospital for "psychiatric evaluation" after someone called about a tweet sent to Moore threatening suicide.
