Facebook's enormous userbase makes it a powerful tool for distributing public service announcements. To maximise this potential, the company is introducing "Child Rescue Alerts" in the UK today, which will appear in your News Feed with crucial information about a recently missing person. Instead of a blanket broadcast, however, Facebook will usually filter these alerts so they're only visible to people nearby. The idea being that if you're within a designated search area, there's a better chance you'll have seen the missing person, or be able to keep a look out for anyone matching their description. Of course, you can also share these alerts to everyone in your network, increasing their reach.