People who know how to program and program in flash. Then you need a developing team and a goal to work around. From there you start getting graphic designers for your game to make it look how you want it to while the code monkeys are making it run like it should. Then you get your promotion guys and put the word out around the web, Civony is on youtube, gaiaonline, various other websites ad space which brings in users and blam.

Here you are.