So, basic recipe:
Take 1 part chat system, and add to 1 part achievement-whore system. Give people achievements for most words typed in a day, people talked to, people talked to simultaneously, people on friends list, people on block list, number of people who have you on their friends list, number of people who have you on their block list, and whatever other completely retarded fail thing you can think of.
Add 1 part avatar design with all the Bell's and whistles, something like what City of X does. Shake well.
You have now covered 50% of Bartle's types, as well as the special super secret fifth Bartle type known as 'fluff whore'. And you didn't even have to make a game! The sad part is, a small part of me knows that if somebody made a program like this (and made it easy to add friends from other social networks), it would probably be wildly successful.