Breaking Down Netherock

I had trouble finding Netherock at first.
Don't go after the map indication, go to the southern parts and you will soon find Netherock, you don't need to summon him or so, just head south instead of south-west.
Soloed him as a level 70 Fury Warrior so if you are the same you won't need other people with you.
Good luck.

He's not too hard, but make sure you clear the area properly. Twice. Then again once more to make sure. Then carpet bomb it one extra time to be safe. If possible, nuke the whole island too. There are about twenty seven million patrols passing through the area, and if you're soloing this guy then the last thing you want is 2-3 adds pounding on you in addition to the adds Netherock spawns himself.

The Netherock Crumblers actually spawn from Netherock's body as you damage him, much like the Raging Colossus's in Hellfire Peninsula, so don't let the crumblers locations on the map confuse you. He was about the same difficulty level as a Colossus, relative to level while in Hellfire.