Pantheon, the Spartan of LOL is an AD based assassin type champion that excels in 1 v 1 duel. Pantheon is best played at top but he can also fulfil the role as a "ganking oriented" jungler (for less competitive and less organized normal games). Pantheon has terrible jungling speed and low sustainability in jungle, so its success and usefulness in the team depend mostly on his early gank during laning phase. Your objective for playing Pantheon as jungler is to suppress the growth of the enemy AP & AD carries during laning phase.
Pantheon Jungling Route = Wolf -> Blue -> (Look for gank in mid >> bot >> top) -> Wraith -> Red -> (Gank Again if not low in pots and Hp) -> Golem -> Wraith -> Base -> Gank again at level 4 with red.
Primary Skill To Upgrade : Q (Spear Shot). Your bread and butter to deal instant burst damage. Master the skill of spear throwing by level 9.
Secondary Skill To Upgrade : E (Heartseeker Strike) (Finish this by level 13 to increase your DPS output)
Tertiary skill : W (Aegis Of ionis) (Only 1 level is sufficient in early gank for that 1 second stun.)
Ultimate : R (Grand Skyfall) (A powerful long distance initiating skill, upgrade this at level 6, level 11 and 16)
Pantheon Pre Level 6 : You must start to look for gank when you hit level 2, put your priority on ganking mid (usually mage with low armor) then bot or top. Ping your lane partner before you gank, initiate the fight with your Aegis of Zonia (1 second stun), then use Spear Shot and Heartseeker Strike (Lvl 3) to inflict heavy damage to the enemy AD/AP carries. If your lane partner is competent enough, he/she shall get a KS (kill secured) from your ganking effort . Repeat the same process when you reach level 4 with red. Do not your waste your combo on tank or tanky support as it will mostly be a waste of time and may even get yourself killed.
Pantheon Post Level 6 : Now you have learned the legendary Sparta Grand Skyfall, you no longer worry about wards placed on the river and bush because you can now throw yourself to the enemy rear side from distant. You shall use it to gank the enemies who overextend even slightly. The OP Sparta Grand Skyfall is best used at Top or Bot lane where there is less space to escape. Initiate with R, immediately ping your teammates for imminent Sky Fall, if you teammates are competent enough, they will start charging towards the enemies. When your skyfall (R) hits the ground and manage to get near one of the clueless enemies, immediately pop your Aegis of Zonia (W) (1 second stun) on the enemy carry, then Spear Shot (Q) and Heartseeker Strike (E) to take out a chunk of his/her health. Your enemy shall witness grey screen when your teammates follow up with their own combos.
Team fight : Pantheon is slightly UP when it comes to team fight due to his mostly single target abilities. But he can still make up this shortfall by carefully selecting his victim, aiming only fed AP or AD carries in team fight. If you are able to kill or assist in killing one of the enemy carries in team fight, you have done your job as a Pantheon jungler. If you find yourself always thwarted by opposing enemy team CC abilities (Ie : Amumu, Sona, Zyra & etc) before you can pop your skills. Consider getting get a Quicksilver Sash for your third or fourth item or as fast as you can.
Watch Pantheon Jungle/Ganking Montage
Summoner spells are Flash & Smite
My favorite items for jungle Pantheon in season 3 are as follow:
Mercury Thread, Wriggle Lantern, Frozen Mallet & The Black Cleaver
Alternative Items to consider
Vs Strong AP : Consider getting Maw Of The Malmortius after Frozen Mallet
Vs Heavy CC team : Consider getting Quicksilver Sash after FM, and upgrade it to Mercurial Scimitar later. Quicksilver Sash provides 45 Magic assistance, and remove all debuffs upon activation.
Pantheon Jungle Masteries 
Runes : 9 X Greater Seal Of Armor, 9 X Greater Seal Of MR, 9 Greater Mark of scaling attack, 3 X Q of Attack Damage.
