A path you want them to go? Well, I shall point you out the important notes of what I ran into when I was doing my Turret map.
First of all, if they're creeps owned by Neutral Hostile, you'll have to go to Advanced >> Gameplay Constants and under Creeps you'll find their wander range and movement range and stuff, which you should set to 99999. The idea is that creeps camp and run back to their original position after moving enough, and usually it becomes upsetting that after they move a distance they suddenly turn around walk back to their spot.
But, the above can be avoided by simply making all of the "creeps" owned by player 12 as opposed to Neutral Hostile.
Now to be more on-topic.
It depends on how complex you want it to be. If it's just walking in a spiral of sorts and there is only one way to go, you can simply order them to move to the destination.
But if you want different paths and such, it gets complicated. You'd have to create multiple destination regions with triggers that make the entering unit, if they're apart of a unit group (add them into the unit group when they're created and remove them once they're told be moved, so that you don't end up telling people of the same unit-type who have different ideas in movement to move to the center), move along to the next destination region.