Yes, I would definitely start incorporating using weights to thicken the abs - I started doing it a few years back and I've noticed a huge difference between using weights versus just relying on bodyweight. My abs have thickened up considerably in this time, they protrude more (not in a bad way), and I haven't even started dieting down (simply because I've got no reason to diet down at the moment).
I tend to do crunches on an incline bench by first warming up using bodyweight only, then work sets involve holding a 5kg plate, then a 10kg plate, then 15kg plate and crunching til failure.
Reverse crunches are usually just performed with bodyweight although sometimes a put a light dumbell between my feet and hold it there whilst repping out.
Also try doing weighted rope pulldowns by crunching the abs in too - they work pretty well.