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.