Before you start, make sure to read the whole text below this text, if this is your first time for pantheon ofcourse, if you are an advanced player you may always read this but i think you know why i chose the items and know what to do, then reading this will only make you closer to perfection.

I start of at top, if you have a premade teammate with you, i recommend the friend lanes with you as a ranged carry (like me a pantheon & ashe combination. Try to get First blood, the runes are especially chosen for having a maximum early game domination with your Spear shot. Also try to get in the bushes BEFORE your opponents. It gives you a better chance of throwing a second one which normally would mean the half of your opponents life.

After you have reached lvl 6, normally i would recommend you recall. Tell your teammate to let them push for a moment until they are almost in front of your tower. use your ultimate right when you are in range for the bushes in the river, then you chose to land a stun on the champion with the least of their health remaining. Land your stun and quickly follow up with your spear, always throw your spear when it is ready. do NOT use your E skill, it is far too weak in mid game, Chase your opponents, giving you more in range possibility for your powerfull spear.

If you are level 15 or beyond and you followed the build path correctly, Pantheon will be a superior offtank in comparison with the rest of the champions, time your stuns and be offensive with your spears to get as many kills as you can.

Starting with doran's blade speaks for itself, giving you health and damage for your early game.
The first bloodthirster is recommended to get it very fast, but the damage of the B.F. gives me enough to sustain my lane with great damage.
The boots i've chosen are not the boots i always pick, i recommend you pick NINJA TABI for AD and MERCURY'S TREADS for the AP opponents.
Then you get the bloodthirster, giving you great life steal & damage to overpower your spear.
The frozen mallet is great, cause it slows the opponents so they stay in the range for the spears and a Big boost in health.
The second bloodthirster will really overpower pantheon, cause if he gets the amount of 2 full bloodthirsters, he is unbeatable with some smart playing on the summoner his/her side.
An iinfinity edge gives almost as much damage as a bloodthirster, and since i've got 2 of those it would be awesome to mix it with the 250 procent critical damage.
An atmas wil give you 60 attack damage extra, with a sufficient boost in armor and the critical strike chance is to get more critical chance for the infinity edge it's effect.