Once again, social networking sites Twitter and Facebook are proving to be lifelines in times of crisis.

A devastating 8.9 magnitude earthquake and then a tsunami rocked Japan early Friday morning. The double disaster is reported to have killed thousands across Japan, and thousands more are said to be missing.

And the quake and tsunami caused massive damage to buildings and roads, as well as electrical blackouts and intermittent cell phone service.

With so many people unable to physically get to family and friends or to even reach them on the phone, countless people in Japan and around the world took to Twitter and Facebook to reach out to loved ones.

"Social communications, like Twitter, and social networking sites, like Facebook, are at their best when big news is breaking," said Ezra Gottheil, an analyst with Technology Business Research.

"They are the means available to almost everybody to broadcast information, to communicate one-to-many," he said. "And, in some cases, they help get around bottlenecks in one-to-one communication."

An hour after the quake hit Japan on Friday morning, Online Social Media, which tracks social media services, reported that Twitter was experiencing 1,200 tweets being posted every minute. And at most times throughout the day, eight or nine of Twitter's top 10 Trending Tropics -- such as #prayforjapan, #tsunami and #japan -- were directly related to the earthquake and tsunami.

Organizations and relief efforts also are taking to Twitter, posting information about everything from emergency phone lines for non-Japanese speakers to tsunami alerts, altered train schedules and lists of shelters for those left homeless.

On Facebook, people not only posted thoughts and prayers for the people of Japan, but used their updates to tell friends and family where they are and how they are doing. Facebook Pages like Japan Earthquake also popped up, grabbing nearly 3,000 followers in about 12 hours.

Brad Shimmin, an analyst with Current Analysis, said today really does show social networks at their very best. "The No. 1 trending topic on Twitter right now concerns the 90999 text message number for Red Cross relief," said Shimmin, who calling sites like Twitter "lifelines."

"From what I've seen today, social networks have brought out the best in people, encouraging them not only to take action but also supporting them in those efforts to bring relief to the victims of this catastrophe," he said.

"While there are so many technologies at this time that isolate us from our fellow beings, social networking tools have shown their ability once again to unify us as human beings, and to bring out what is most altruistic and empathetic in our natures," Shimmin added.

This isn't the first time that people have turned to Twitter and Facebook during trying times. The social networking sites became lifelines for people during the massive earthquakes in Chili and Haiti last year .

They also were key communication tools during the 2009 government crackdown in Iran, as well as when a U.S. Airways plane made an emergency landing in New York's Hudson River.