Reaction swift to Boston Marathon tragedy

Word of the Boston Marathon bombings spread worldwide within minutes via social media Monday, with photos, videos, eyewitness accounts and reactions filling feeds everywhere.

There were more than 7.5 million social and digital media mentions of the marathon, the two explosions and the aftermath in the 24-hour period ending at 9 a.m. ET Tuesday, according to data from the Salesforce Marketing Cloud, a social marketing suite. More than 7.2 million of those mentions were via Twitter.

Steve Silva, a sports producer for boston.com, shot video of the explosions that was picked up by media outlets worldwide. His tweet was one of the first from the scene.

Athletes from Boston and around the world posted their support of the city, the marathoners and those who helped.

Wide receiver Danny Amendola, who joined the New England Patriots in March, launched his fundraising effort.

Those in Hollywood and elsewhere who call Boston -- or in this case, nearby Cambridge -- home also offered their support:

Witnesses offered firsthand accounts on Twitter, Facebook, Instagram and reddit. Among them was South Carolina's Demi Knight Clark, 36, who like thousands of others was running the race to raise money for charity. The bombs exploded as the 4-hour mark of the race approached -- the time when many charity runners usually plan to finish.

Clark's charity work helped her earn VIP passes for her husband and two children, who were watching her approach the finish line in Copley Square on Boylston Street when the first blast occurred. No one in her family was hurt, although she temporarily lost her hearing.

"It was like a war zone," she said Tuesday on "Good Morning America."

Linda Leonard Ambard is a physical education teacher who lost her husband of 24 years, Air Force Maj. Phil Ambard, in an attack in Afghanistan in 2011. Her Facebook post detailing the scene at the finish line of the race has been shared nearly 15,000 times and received more than 79,000 "Likes."

"I was but a quarter mile from the end when I heard a loud boom, felt the street shake, and started to smell a smell I never smelled before. All hell broke loose," she wrote. "People were screaming and sprinting away from the finish line. The race immediately ended. For me, a girl who was invited to run to (honor) her soldier... it threw me back into a spot where I immediately felt out of control, that my life was being torn apart, and I stood (immobilized) sobbing."

Reddit user 99trumpets, who identified herself as one of the Gatorade girls at the finish line, posted this account of the bombing on the running subreddit and received more than more than 1,000 comments.

"Suddenly a big BOOM, absolutely thunderous. I was looking right at it, huge plume of smoke ... I thought, "That's not gunfire" (I've lived in Rio, I know gunfire). BOOM, another one, I said "That was an explosion" (duh, I know)," she wrote. "I was at the point where everybody has just stopped running and is savoring victory and EVERYBODY STARTED RUNNING AGAIN - something about this scene was absolutely surreal, to see all those exhausted runners who looked like they could barely walk, just all spring back into action simultaneously like that."

Dick and Rick Hoyt, a father and son team participating in their 31st marathon, were about a mile away from the finish when the blasts occurred. Rick is a quadriplegic who was born with cerebral palsy and is pushed in a wheelchair by his father. Through his Facebook page, Dick Hoyt said that he and Rick were not hurt, and offered his well-wishes to those who were injured. Blind runner Ron Hackett and his guide, Tim Scapillato, who posted their inspirational story on Facebook Monday, both also escaped injury.

Bill Speros is an ESPN.com contributor. He can be reached on Twitter @billsperos or via email at bsperos1@gmail.com.