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. Phone companies say service is operating, but with heavy traffic.
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.
Google Person Finder
American Red Cross