During all the chaos following the blasts, panic and fear set in.
People quickly tried to find friends and loved ones.
As cell phone towers around Boston jammed, social media played a key role in helping locate hundreds of people.
It's what Michael Halpern used Monday.
"I have a bunch of friends and co-workers who had a reason to be down there that day. Whether they were running or watching the race, my first thought was as to their safety." Halpern said.
Like thousands of others after the bombings, Michael was desperate for answers about his friend Sarah, from Tampa.
Halpern said, "I had Facebook open and was checking that. Her sister did post a message about Sarah's safety. I thought that was the point to pay it forward and share the fact that she was safe on other networks people might go to."
Shortly after the blasts, Google launched "Person Finder." It's a digital tool that helped people track information about loved ones and it's simple to use.
People could quickly enter data if they were looking for someone or had information about someone at the race.
Halpern said, "I think that people should make use of all the tools available to them to find out what's really happening on the ground."
Within minutes of the launch, word about ‘Person Finder' spread on Twitter. Users urged others to retweet and use the location tool. At last check, Google's Person Finder logged more than 5,300 records.
The Red Cross also launched a similar site called "Safe and Well." Within seconds of entering information on the site, friends and family have instant access of your well being, during a disaster.
Janet McGuire from the Red Cross Tampa Bay Chapter said, "It connects you up with your social network. So, if you have a Twitter or Facebook account, you can connect that, too. It will send that message out that I know I'm ok. You know I'm alright."
"It's interesting that people seem to be coached now about how to use technology in a way that benefits others," Halpern said.
To check out Google's Person Finder, follow this link: http://google.org/personfinder/global/home.html
To check out "Safe and Well" from the Red Cross, follow this link: http://www.redcross.org/find-help/contact-family/register-safe-listing