A web app called emojitracker, first released in late July 2013, shows in real time how frequently emojis--small, emoticon-like icons--are being used on Twitter. The app was developed by New York-based rocket news.
As of July 29, the single most used emoji on Twitter is "black heart suit," which depicts a red heart on a deck of cards. It's been used more than 65 million times, more than twice as many times as second place "face with tears of joy."
I'm happy [that emojis have become so popular], but to be honest, it's not something I'm really cognizant of. It's just too big, you know.
– Shigetaka Kurita, emoji creator
Kurita, who invented the emoji while at Japanese telecom NTT Docomo, noted in a lengthy March 2013 profile in The Verge, that the casual nature of online communication, helped convinced him to create emojis.