Since I'm new it would take a long time to make an example up, but you should be able to detect whether the enemy is close enough using something like this:
That's what I used in my rpg to detect whether a caveman is close enough for the hero to talk to. As for chasing I'm working on the same thing, experimenting with bullet and 8-dir behaviors. Leaning towards bullet. You can set the enemy's angle towards the player every X ticks and set it to move forward till its in range.