I'm not really sure what he needs, but reducing his cooldowns and/or maybe increasing his damage slightly (either base damage or scaling) would be a good place to start. He's been trash tier for far too long.
http://champion.gg/statistics/#?sortBy=general.winPercent&order=descend
Subject 51 votesVolibear drops to all fours to hunt his enemies, gaining 15% Movement Speed for 4 seconds. This bonus is enhanced to 30/35/40/45/50% Movement Speed while moving toward enemy champions.Volibear's next attack during this time deals an additional 30/60/90/120/150 physical damage and flings the target behind him.
CHANGES
Volibear drops to all fours to hunt his enemies, gaining 25% Movement Speed for 6 seconds. This bonus is enhanced to 30/35/40/45/60% Movement Speed while moving toward enemy champions.Volibear's next attack during this time deals an additional 30/60/90/120/150 physical damage and flings the target behind him. Flinging a minion or jungle monster and killing it resets the cooldown and refunds the mana cost, flinging a champion refunds the cooldown by 50%
To be fair - even if Voli was strong, right? Like most of every champion has a way to avoid him. He'd basically be a VERY good pick into very niche champions like:
basically champions without gapclosers or relatively lacking them 
KoKoboto1 votesThey nerfed frenzy awhile back:
V6.13 Frenzy.png Frenzy Base damage reduced to 60 / 110 / 160 / 210 / 260 from 80 / 125 / 170 / 215 / 260. Bonus attack speed per stack reduced to 4 / 8 / 12 / 16 / 20% from 8 / 11 / 14 / 17 / 20%. Maximum attack speed reduced to 12 / 24 / 36 / 48 / 60% from 24 / 33 / 42 / 51 / 60%.
They could revert that. Some small changes would be nice until he gets a full VGU.
Eedat1 votesUmmmm you're looking at his top lane winrate. His jungle winrate is 52%. Doesn't need any buffs, sorry
