Apparently, my Locust build was a pretty amazing support.
Witch Doctor - Game Guide - Diablo III
My strategy was to run and Spirit Walk into the middle of the mob, do a quick Soul Harvest and Locusts before I run back out. Once I break from Spirit mode, I lay down a Grasp of the Dead to help slow them down before I start to take my spot to shoot darts and DPS. Locusts is Pestilence only because my current weapon only offers +Poison damage, and if I using Searing Locusts it won't get the same damage increase since it's Fire-type (at least, if I'm understanding this correctly).
It works great since I'm packing 18k base DPS with this really awesome Staff I ended up buying with a base 1.3k DPS and a couple damage mods on it. The hefty damage plays very well with Locusts and Grasp of the Dead since the damage isn't that reliant on the overall DPS rather than the bulk damage it will do. Both skills do % damage over a set amount of time.
I've also got some attack speed mods on my gloves, ring, and amulet which helps make Poison Darts a decent single-target option. My other choice would probably have been to use Haunt or Spirit Barrage, but they make me too mana-starved for it to be efficient.
I've also realized that I die too quickly, even when I pack on the Vitality and some resists so I re-gemmed all my Amethyst gems into Topaz so I can get more Intelligence for damage and resistances. I still die just as much, but at least my Locusts can tick off more than they normally do.
(I'll post my set-up tomorrow when I'm able to get back on Diablo.)