If you need to contact someone in a hurry, don't use Facebook or any other social media unless you know for sure the person is used to getting messages that way.
Facebook is huge. It has 1.6 billion users. Facebook and its assorted apps account for about 30 percent of all US internet use.
Given those numbers, your message stands a good chance of getting through.
With a billion people spending 20 minutes a day on the site, statistics say your message should reach its target sooner rather than later.
Yet not every person is on Facebook. Not even in the world's rich countries . Not all of the people with Facebook accounts are frequent site visitors. Not all are, to use the popular jargon, engaged.
So unless you know your target will read your message before too long, Facebook not the best way to send important messages. It can be hit and miss.