Facebook and Twitter devotees often use the online networking tools to post gossip and idle details about their lives. But the sites have also become a crucial means of communication during disasters like the shooting that unfolded in a German town Wednesday morning.

Shortly after a teenage gunman killed 16 people including himself, users were sharing news of the tragedy and posting condolence messages.

One user of the micro-blogging website Twitter tapped out text messages saying his girlfriend who lived in the town, Winnenden, had just phoned to say there was rampage at a school and that she was afraid to leave her office. She was then tracked down by a French news agency to give an account of her experience.

Also in the immediate aftermath of the shooting, Twitter users from around the world began reaching out to the town.

"Prayers for the victims and families of the German school shooting," wrote one person.

It's a scenario that has been played out in other recent tragedies, such as last year's terrorist attacks in Mumbai and the US Airways crash in New York's Hudson River.

Social networking tools allow people to instantly share their grief, says Jeannette Sutton of the University of Colorado's Natural Hazards Center.

"What more can you do when there's this kind of destruction of human beings other than saying, `I care and I am sad,"' said Sutton.

The sociologist has studied how social networking plays a role during disasters, beginning with the shooting at Virginia Polytechnic Institute two years ago when a student killed 32 other students and professors and then turned the gun on himself.

"What we've seen in disaster research for 60 years now is that people converge to a disaster, but we're seeing them converge now online," said Sutton.

She said her research shows that people are using social networks to share information, ask questions, organize donations and encourage each other.

Sutton and another colleague also studied online forums and news sites to see how people were communicating during the wildfires that ravaged Southern California in the fall of 2007.

Web developer Nate Ritter turned to Twitter, with its limit of 140 characters per message, to get out information more quickly than his blog posts.

"I was using Twitter but didn't understand what it could be used for until this happened," Ritter said from San Diego.

"I found it very powerful," he said, adding he had 350 followers on Twitter during the fires.

Toronto Mayor David Miller has been using Twitter since last December. He said his city will use social media to add to the ways it's already reaching citizens during emergencies.

"I think Twitter, Facebook and other social networking media significantly add to our capacity to get the facts out in a simple, calm, clear way," Miller said.

The American Red Cross, Homeland Security and Los Angeles Fire Department are among public organizations using Twitter in the United States.

Sutton will speak at the World Conference on Disaster Management in Toronto in June about the role social media networks play in disaster communications and how public officials can use them.