Many Facebook users think about a common topic. That's , how to send a message to all Facebook friends at the same time. But Facebook does not let to send a message to all friends. You can send a message to only 20 friends at this time. If you want to do this just click the Message button located on the top of your profile picture. Then click Send a New Message. Then start typing your friend's name in To: box and select your friend whom you want to send a message. Then beside your selected friend's name again select another friend by typing the first letter of his name. Then add another. Thus, you can add 20 friends to send a message. Then compose your message and send it to your selected 20 friends at the same time.
But at the time of writing this post I tried to send more than 20 friends. And I became successful to send 35 friends. You can also try it. I think, at present Facebook lets to send a message to more than 20 friends.