Google has set up a people finder to help find loved ones at google.org/personfinder/2013-boston-explosions.
Local residents are offering free places for marathon runners to stay at Boston.com.
Twitter hashtag #prayforboston is being used to offer condolences and thoughts on the explosions.
YouTube users have uploaded videos of the explosion. Two can be seen here and here.
Follow @BostonMarathon and @Boston_Police for the latest official news updates.
