We had a bumper week on the website at work thanks to a very effective Facebook post that has blown away any other website marketing push we've had. What was surprising was the amount of mobile traffic. When I took this photo, the stats were: 84% mobile, 11% tablet and 6% desktop. A few minutes later there weren't any people on desktops accessing the site.
Still don't think you should have a mobile responsive website? Think again. Especially if you're using Facebook as a promotional/engagement platform.