Social-media companies Facebook Inc. and Twitter Inc. provided new tools allowing people around the world to track and discuss the violent attacks in Paris on Friday with unprecedented speed and depth.

Facebook activated its “Safety Check” feature Friday, allowing the site’s users in the area of the attacks to mark themselves as safe on their profiles. This marked the first time the tool was enabled for violent attacks. Twitter’s news-curation tab, known as “Moments,” featured tweets, images and videos from news agencies and...