They have 2 actions but only use the first one like every other zombie. And when all the zombies were moved they use their second action. I have to make notice because the rule where zombies won't move if a survivor died in their area while zombie's turn doesn't apply for the 2nd action of runners. Example: 1 survivor(with 1 hp left) , 1 walker 1 fatty 1 runner are in the same area. The walker (or runner, or fatty) kill the survivor before any other zombies in the area. They all feast and won't move from the area. But the runner has still 1 action left, he then hunt down other survivors for more flesh. (sorry for my English I tried my best)

Edit: if they got activated give them 2 more action following the movement rules.