Well, you are not calling the moveTowards()
in any loop -> the position is not updated. Or where exactly are you updating the enemy's position? I see only one setting of .x, .y of enemy and it is right after you create the object, no further updates.
Put this into your loop function in Main.as:
for(var i:int=0; i<enemies.length; i++) {
Enemy(enemies[i]).moveTowards(player.x, player.y);
}