Chicago: Far-flung family members, co-workers and friends frantically used social media, mobile phones and even a “people finder” website on Monday to try to learn the fate of participants and spectators at the Boston Marathon, where three people were killed and dozens injured after a pair of bombs exploded near the finish line of one of the world’s great races.

The search was made more difficult because heavy mobile phone use caused slow and delayed service. In an age connected by everything digital, the hours after the blasts produced a tense silence.

At the race, 51-year-old Julie Jeske, of Bismarck, North Dakota, had finished about 15 minutes before the explosions and was about two blocks away when she heard two loud booms. She immediately tried to call her parents but could not place the call. A friend was able to post on Facebook that they were OK, but reaching her parents was another worry.

“I wasn’t able to call and I felt so bad,” Jeske said. “When I was finally able to reach them, my mum said she was just absolutely beside herself with fear.”

On the other side of the continent, in Seattle, Lisa Cliggett was waiting for any word from her brother and sister-in-law.

Mark Cliggett, 51, and his wife, Dr. Janet Vogelzang, 54, have run several marathons together and always send their sons text messages after crossing the finishing line. On Monday, those messages didn’t arrive and the couple could not be reached via mobile phone.

Lisa Cliggett said she went to the marathon’s website and tried to calculate where the couple should be based on their last locations and running speeds. She decided they should have already finished the race when the blasts hit.

“The question is, do you loiter around the finish line?” she said. “And where was the bomb?”

Finally, about three hours after the blasts, the couple called their sons to tell they were unhurt. Matt Cliggett sent his sister a text that said, “We were about 100 yards from second explosion. Sad day.”

Google also stepped in to help family and friends of runners find their loved ones, setting up a site called Google Person Finder that allows users to enter the name of a person they’re looking for or enter information about someone who was there. A few hours after the explosion, the site indicated it was tracking 3,600 records.

Mary Beth Aasen, of Shorewood, Wisconsin, and her husband were using an app to track their daughter Maggie’s progress along the marathon route. They didn’t realise anything was wrong until a worried friend texted Aasen and asked if Maggie was OK.

The app indicated that Maggie was still moving, a relief for her parents. Mary Beth Aasen tried in vain to call her daughter for about 30 minutes before Maggie called her.

“When I talked to her she was pretty upset,” Aasen said.

Kim Hauser, a substitute teacher in the Chicago area, did not know about the explosions until her students went home and she got a chance to look at her phone. There were messages from acquaintances asking, “Is your brother OK?” She searched the news and it dawned on her why they were asking.

“I tried to call him immediately, but there was no cell service,” the Frankfort, Illinois, woman said. “I waited anxiously by the phone. I just felt horrible. I had a hard time holding myself together.”

Five minutes became 10, then 20 — finally, 45 minutes later she looked down to see a text from her brother, Thomas Wiora. He had crossed the finish line shortly before the explosion and was 120 yards away when it went off. But he was fine.

“I was relieved,” she said. “But the whole thing was so heartbreaking.”

Mary Butler, of Oklahoma City, hadn’t been able to reach her husband, Jason, who was running with his son, brother and other family members. But she said he’d posted on Facebook that he and the others were OK.

“That’s all I know about it,” Mary Butler said, adding she’d been trying to call since she’d first heard of the explosions. “I’m just waiting — keep trying to call.”

She declined to talk further so that she could keep her phone line open.