Raycast is not likely to help you much here. There are several possible approaches, with the simplest probably being this:
1) Put an Area2D on the enemy and connect its entered/exited signals.
2) When the player is inside this detect area, move towards it. To move towards something, you find the vector pointing to the target:
var dir = (target.position - position).normalized()
If you'd like to see a more detailed example of this, see here:
Godot Recipes: Chasing the player