People used Facebook and other websites to try to find friends and family missing after the earthquake in Haiti this year. (Jorge Saenz/Associated Press)

About one in five adults in the U.S. say they would use Facebook or other social media to try to contact emergency responders in a disaster, a new survey suggests.

The American Red Cross online survey asked 1,058 adults about their use of social media sites in emergency situations when they couldn't reach 911.

"The first and best choice for anyone in an emergency situation is to call 911," Gail McGovern, American Red Cross president and CEO, said in a release.

"But when phone lines are down or the 911 system is overwhelmed, we know that people will be persistent in their quest for help and use social media for that purpose."

Respondents said if they knew of someone who needed help:

• 44 per cent would ask other people in their social network to contact authorities.
• 35 per cent would post a request for help directly on a response agency's Facebook page.
• 28 per cent would send a direct Twitter message to responders.

Nearly 70 per cent of those surveyed said emergency responders should be monitoring social media sites to send help quickly, and nearly half believed an agency is probably already responding to any urgent request posted.

Of those surveyed, 74 per cent said they expected help to come less than an hour after their tweet or Facebook post.

Social media sites were the fourth most popular source of emergency information after TV news, radio and online news sites.

More respondents said they got emergency information from social media than from official government websites or emergency text message systems.

One in five said they post eyewitness accounts of emergency events.

The Red Cross commissioned the survey ahead of a summit on Thursday in Washington devoted to finding better ways to handle online information during disasters.

The Red Cross said the survey was representative of the adult population in the U.S. It was conducted on July 22 to 23 by Infogroup.