Just have at this build. Loads of health. LOADS of damage with w (roughly 1000 base damage with charge warmogs). Uber tanky because of the high health (especially when you get the Warmogs charged up). His runes give him balance. Cleanse is good, dont be afraid to use it often. Use heal after passive kicks in or if your team needs it in a team fight. That pretty much sums it up.
This build is very effective, stick to it. Your Volibear won't only be tanky, he'll be a threat too.
Note: MobaFire didn't calculate health very well, should be around 6000 with uncharged Warmogs, 7400ish with charge.