Is there a range at which they will be activated or do they follow the player if his back is turned like in Mario?
You can make an ivisible detector like a big circle which is positioned always at the enemies X,Y coordinate, and if the player is overlapping the detector make the enemy "always look in direction of player, start movement" (assuming the enemy is using bouncing ball movement). If it will be based on where the player is facing, rather than a range detection... you would have to do something like:
-Enemy X is greater than Player X and Player is direction "left" then
-enemy look at player, start movement
-Enemy X is less than Player X and Player is direction "right" then
-enemy lok at player, start movement
something along those lines. Forgive me if I am not making perfect sense... I'm a little tired after a long day
You might also want to check out the fantastic "Last Known Pursuit" method for your enemies. I've used something very similar and it's a big improvement over enemies that mindlessly chase you until the end of time.