See KY語 in Wikipedia. There is even a dictionary for this type of words, but this trend is something in the past, and most of them are completely forgotten.
As of 2019, ones that are still sometimes used include:
mjd?: マジで? "Really?", "Are you sure?"
ktkr: キタコレ "Yay!", "Here it comes!"
kwsk: 詳しく "Tell me more about that."
ggrks: ググレカス "Google ...