A suicide note on Moore's Twitter site generated 911 calls from all over the world. Those calls enabled San Jose police to locate the woman before she could hurt herself.
At about 4:30 a.m., San Jose police dispatch began receiving 911 calls that someone in the Silicon Valley was going to take her own life.
"We received numerous phone calls from all over the country and the world. Places as far as Boston, New York, Australia and Canada," said Sgt. Ronnie Lopez, spokesperson for the San Jose Police Department.
The callers were followers of Moore's Twitter feed. Twitter is a social networking micro-blogging service that enables its users to send and read other users' messages, called tweets.
The San Jose woman who uses the name "Sandieguy" on Twitter, sent out a suicide threat to her 554 followers. It included Moore's Twitter name, "mrskutcher."
Moore came across the threat and re-tweeted it to her 384,000 followers across the country. Many of them called San Jose Police.
"Sandieguy's" threats seemed real to Moore, and included this tweet: "Getting a knife, a big one that is sharp. Going to cut my arm down, the whole arm so it doesn't waste time."
Based on the information police received, they were able to find the woman's home. The woman was not hurt. She was admitted to a hospital for a psychiatric evaluation.
Moore posted an update on her Twitter feed. "It is my understanding that the situation was not a joke and that through the collective efforts here, action was taken to provide help," she said.
Moore's husband, actor Ashton Kutcher, posted a message about the incident on his Twitter page. "Wifey reported a suicide attempt based on a at reply tweet she got and saved someones life. The woman is in the hospital now," he wrote.
By late Friday, Moore had posted the following tweet: " Good Night Twitterers-this day has been an extraordinary. I am taking pause to reflect on all the blessings I have in my life Thank you!!"
Police say they understand why people now prefer to e-mail or tweet, but emergencies are different.
"In times of crisis or in times of need, we are requesting that you use the traditional sources -- 911," said Sgt. Lopez.
"They should seek help from the people who can best provide it, which would be either a suicide hotline or 911," said Dr. Clark Hinderleider, a mental health care advocate.
Was Moore one of the 911 callers? If she was, police say she didn't identify herself.
Moore Is Latest Star to Make News Via Twitter
Twitter also did not immediately respond to requests for a comment regarding the incident.
Moore is the latest celebrity to make news via Twitter. A fashion designer filed a lawsuit against Courtney Love last week, claiming the rocker used the micro-blogging network to disseminate "an obsessive and delusional crusade" of malicious libel against her.
When Lance Armstrong crashed his bike during a race in Spain in late March, his Twitter followers found out about his broken collarbone before much of the rest of the world. The seven-time Tour de France champ also used Twitter to post a photo of himself in a hospital bed minutes before he was wheeled into surgery.
Moore's husband, Kutcher, is one of Hollywood's most avid Twitter users, boasting a following of more than 600,000. He posted a photo of Moore's age-defying behind on his Twitter feed in March, along with the message "Shhh!, don't tell wifey."
ABC News contributed to this report