Starting with the most popular emojis, these include the obvious 😂 Face With Tears of Joy and 😍 Smiling Face With Heart-Eyes (popular on all platforms), but the addition of the 🎂 Birthday Cake does hint at one common theme on Facebook.
Above: Most popular emojis used on Facebook and Messenger. Image: Facebook.
Breaking down the top emojis by country reveals Australia and Canada to be the most keen on birthday greetings.
Above: Some of the least used emojis on Facebook. Image: Facebook.
Rounding out the statistics are some raw numbers on emoji use. I'd have liked to see these in context (what percentage of messages sent on Messenger contain only emojis without other text), but nonetheless having nearly 1 billion emoji-only messages sent each day is a staggering number for a character set that wasn't universally exchangable until 2010.
I put “some” in quotes as it seems likely these have been chosen to present some of the more interesting yet lesser-used emojis. I would imagine that if Keycap #1 is shown as least-used, so would the other keycaps. ↩︎