The site, called Google Person Finder, allows users to enter the name of a person they're looking for or enter information about someone who is there.
Cellphone use has been difficult in the Boston area. A law enforcement official says cell service was shut down to prevent any possible remote detonations of explosives. The official spoke on condition of anonymity because the investigation was ongoing.
Far-flung family members and friends are frantically using social media to check on the safety of runners and spectators after two bombs exploded near the finish line of the marathon, killing two and injuring dozens.