Pantheon's early game is by far one of the best, but as soon as mid-late game comes up you lose youre edge. This is the build i use to help later games, its not the most damaging build but you should be able to survive a good while in team fights.

Because burst casters destroy panth i choose the maw of malmortius, it gives you a nice cushon when you get bursted and provides decent ad. Warmogs and atma combo gives you armor, health and attack damage, i dont worry too much about the critical strike end of it since you crit when their life is low, so you can trade atmas for another ad item if you so choose. Last whisper for when they are stacking armor against you, you may get it before bloodthirster depending on the situation. My boots of choice is the beserker greaves, if you are getting fed and pushing turrets the extra attack speed is great, my other choice is merc treads.

For the most part i use flat runes except for health per level seals. armor pen Quints, flat dammage marks, and flat attack speed glyphs. early feeding shouldnt be a problem unless you have bad teams.

21/9/0 are the masteries i use for early game ownage.

I did a match with my pantheon build, it was a 3 v 5 match two of my teammates dc'd, and we ended up losing but i still had a score of 16-9-6, try out this build you will enjoy being able to drop your skills and survive to fight some more.