JOPLIN, Mo. - Emergency crews drilled through concrete at a ruined Home Depot, making peepholes in the rubble in hopes of finding lost shoppers and employees. A dog clambered through the shattered remains of a house, sniffing for any sign of the woman and infant who lived there.

Across devastated Joplin, searchers moved from one enormous debris pile to another Tuesday, racing to respond to any report of a possible survivor.

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 anyone 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.

For Milissa Burns, hope was fading that her 16-month-old grandson, whose parents were both hospitalized after the tornado hit their home, would be found. She showed up Tuesday 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 911 a million times. I've done everything I can do. He was so light and little. He could be anywhere."

Also Tuesday, the National Weather Service announced that the twister that crippled Joplin was an EF-5, the strongest rating assigned to tornadoes, with winds of more than 200 m.p.h. It was the deadliest single twister since the weather service began keeping official records in 1950 and the eighth-deadliest in U.S. history.

Besides the search for loved ones, 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 Tuesday evening.

Meteorologist David Imy said conditions were ripe for severe thunderstorms, including tornadoes, in parts of Kansas, Missouri, as well as nearly all of Oklahoma. A twister hit at evening rush hour Tuesday in Oklahoma City. Seven people were reported dead.

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

Authorities announced a curfew from 9 p.m. to 6 a.m., with only residents and emergency workers allowed inside the disaster zone. People in the Joplin area and beyond have turned to online social networks to find family members missing since the tornado or to learn about the plight of survivors.

Multiple Facebook pages created since the tornado are filled with requests for information about specific people who have not been heard from since Sunday. Some pages include photos of the missing. Other posts share the news about Joplin residents who are alive and well.

Several social-networking efforts specifically focused on finding information about Will Norton, a teenager who vanished on his way home from his high school graduation ceremony. His family had made an appeal on CNN's program 360 with Anderson Cooper on Monday night. 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.

In the waiting room of Freeman Hospital, Debbie McMurry and Dan Perry sat waiting for any news about their 76-year-old mother, Mary Joyce Perry. She was chatting online Sunday afternoon with McMurry when the lights began to flicker in her home, McMurry said Tuesday. When McMurry arrived that night to check on her mother, Perry's home had been flattened.

Dozens of relatives and friends have called hospitals throughout the region. Meanwhile, her family members continued to wait at Freeman.

"Who knows?" Dan Perry said. "She could be anywhere."