Make hordes of NPC (zombies) pathfinding smoother

I have an FPS zombie shooter game witch has zombies, so the question is what is the best (performance level) way to make pathfinding to the player? Max zombies are 25 in a single time.

Currently, I have a renderStepped function that checks the closest player and it the while loop every second it fires a module I have downloaded to make paths (before I used the module, I created a new path every second and waited until NPC moves to the first waypoint and then create a new path and then repeat).