FARGO, N.D. — When Kevin Tobosa got word Thursday that a friend needed help building a sandbag dike, he immediately posted a status update on his Facebook page: "Heading to 2825 Lilac Lane in North Fargo — needs to be raised another 2 feet."
When city officials needed volunteers at other dikes, Tobosa suggested setting up a Facebook group. By Thursday, it had attracted more than 4,550 members and was constantly picking up new ones.
"We really need volunteers again today to get the dikes buttoned up and fill the rest of the sandbags," read a message sent to the group Thursday.
Social-networking sites such as Facebook and Twitter have become vital tools for volunteers as they wage a desperate, round-the-clock battle to protect Fargo from the river and spread the word about rising floodwaters.
"Oftentimes, the government Web sites and phone lines are overloaded and don't have the capacity to answer all the queries," said Jeannette Sutton, a University of Colorado sociologist who has researched the use of social networking in emergencies.
"A site like Facebook is so robust, it has the strength to support this kind of usage," she said.
As the river rose higher, thousands of weary volunteers scrambled Thursday to extend the city's dikes by another foot. Their work was made more difficult by temperatures below 20 degrees that threatened to weaken the effectiveness of the sandbags, which do not stack as tightly if frozen.
The city of 92,000 also announced a potential evacuation plan, and at least four nursing homes began moving residents elsewhere. In rural areas south of town, crews rescued residents stranded by the floodwaters.
By midday, the river had risen to almost 39 feet above flood stage. It was expected to crest Saturday at 41 feet, possibly breaking a record of 40.1 feet set in 1897.
Tobosa, 34, said he learned to appreciate the speed and efficiency of social networks at the online marketing company he owns.
"I use it to reach customers, so I thought why not use it to reach volunteers?" he said.
Property owners on the front lines of the flood fight are also using technology to issue last-minute pleas for assistance.
When Jamie Sampson needed help at her family's home shoring up a sandbag wall, the 26-year-old woman sent a blast e-mail to co-workers and friends, and a friend sent out a mass cell-phone text message.
About 20 people showed up within three hours.
Besides serving as a handy tool for marshaling volunteers, social-networking sites also offer a close-up view of the action for people who are interested but do not live nearby.
Troy Elseth, a 29-year-old software engineer in Mountain View, Calif., attended college in Fargo and plans to move back this spring. In recent days, he found himself obsessively checking a Web site that updated the level of the Red River.
"I realized a quick way to check it would be to set up a Twitter feed," said Elseth, who just closed on a house next to the river. "Naturally I'm pretty interested in the flood level."
Twitter allows users to post a constant stream of sentence-sized thoughts, observations and information.
Elseth posts the Red River's flood stage once every hour or so, information that then pops into the inbox or onto the cell phone of those who subscribe to his feed. By Thursday, his "redriveratfargo" had more than 300 followers, updated almost hourly as the Red River climbed toward its projected crest of 41 feet above flood stage.
Sutton, the sociologist, first noticed widespread use of social networks in a crisis during the aftermath of the 2007 Virginia Tech shooting.
She said many people, particularly younger ones, get all or most of their news about the flood through social networking. She said such sites sometimes do fall prey to con artists, but studies have shown that's rare in natural disasters.
"Once you get to the recovery stage, and people are dealing with FEMA and insurance companies and contractors, that's when you'll really have to be more careful about bad information being spread," Sutton said.
Because of the informal nature of social networking, there's also room for users to show a little personality. That's what Tobosa did early Thursday after a long day on the sandbag line.
At 12:52 a.m., he posted: "Done bagging for the night. Step 1: Scotch. Step 2: Bed."