If we look at the wikipedia definition of social media, it states: "Social media are interactive technologies that allow the creation or sharing/exchange of information, ideas, interests, and other forms of expression via virtual communities and networks"

I personally view the old IRC (Efnet!), BBS, chat rooms, ICQ as the earliest form of social media. And just as addictive - I couldn't wait to get home from school and jump into a chat room. I checked it as often as I did Facebook later on.