JOPLIN, Mo. - Emergency crews drilled through concrete at a storm-ruined Home Depot, making peepholes in the rubble, hoping to find lost shoppers and employees.

A dog clambered through the shattered remains of a house, sniffing for any sign of the woman and baby who lived there.

Across devastated Joplin, searchers moved from one enormous debris pile to another yesterday, racing to respond to any report of a possible survivor, and many turned to social networks in their hunt for loved ones.

The human toll rose to at least 122 dead and 750 people hurt. But just nine had been pulled alive from the aftermath. Searchers fought the clock because anybody still alive after the deadliest single tornado in 60 years was losing precious strength two days after the disaster. And another round of storms was closing in.

People in the Joplin area and beyond have turned to online social networks to find family members missing since the tornado.

Multiple Facebook pages created since the tornado are filled with requests for information about people who have not been heard from since Sunday.

Several social-networking efforts specifically focus on finding information about Will Norton, a teenager who was reportedly sucked out of the sunroof of a car on his way home from a graduation ceremony.

More than 10,000 people have supported the "Help Find Will Norton" community page on Facebook, and Twitter users were tweeting heavily about the missing teen.

For Milissa Burns, hope was fading that her 16-month-old grandson, whose parents were hospitalized after the tornado hit their home, would be found.

Burns showed up yesterday at a demolished dental office near the child's home to watch a search team. At one point, a dog identified possible human remains, prompting eight searchers to dig frantically, but they came away with nothing. Burns was weary but composed. Her daughter - the boy's aunt - sobbed next to her.

"We've already checked out the morgue," Burns said. "I've called 9-1-1 a million times. I've done everything I can do. He was so light and little. He could be anywhere."

Also yesterday, the National Weather Service announced that the twister that crippled Joplin was an EF-5, the strongest rating assigned to tornadoes, with winds exceeding 200 mph. Scientists said it appeared to be a rare "multivortex" tornado, with two or more small and intense centers of rotation orbiting the larger funnel.

It was the deadliest single twister since the weather service began keeping official records in 1950 and the eighth-deadliest in U.S. history.

Another top job was testing the city's tornado sirens to make sure they were operable ahead of another round of potentially violent weather starting last night and expected to last into today in some places. Emergency officials warned jittery residents well in advance of the test.

David Imy, a meteorologist at the federal government's Storm Prediction Center in Norman, Okla., said conditions were ripe for severe thunderstorms, including tornadoes, in parts of Kansas, Missouri, Arkansas, Texas, Kentucky and Tennessee, as well as nearly all of Oklahoma.

Throughout the search efforts, new reports emerged of clusters of victims: 11 people dead in a nursing home, three bodies found in an Elks lodge.

The tornado tossed three vehicles into the Greenbriar nursing home and left nothing more than a 10-foot section of an interior wall standing. On the night of the twister, the Joplin Elks Lodge had been scheduled to host its weekly bingo game.

"If that had been two hours later, there could have been 40 or 50 people in there," said Chris Moreno, a hospital lab technician coordinating an outdoor triage center.

Jasper County's emergency director, Keith Stammer, said the scope of the destruction was making it difficult to account for people affected by the storm. He suggested that many survivors, with nowhere to go, left Joplin for Kansas, Arkansas, Oklahoma or other parts of Missouri.

"There's a lot of confusion, a lot of inability for folks to communicate," he said.