Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
AP Kennen is to me, from far, the best champion to use in LeagueOfLegends. It's small(I call him little ken :P), he sends shuriken, and in his class skin, he's amazing running, it's awesome.
I will leave you my build, I think I've never done negative score since I've mastered it...
In my opinion, I take always mid, because if you have runes I have, at level 3/4 you might have 40AP without any AP item...
For lanes, Kennen it's really awesome too, cuz he can be a kind of carry for lane phase fights, because of his 'Lightning Rush' he can just pass through the enemies and than apply an 'Electrical Surge).
Always remember this: At Kennen's 5th attack deals magic damage, as the way you evolve the skill, it gains more % of magic damage, that's why I evolve it and 'Thundering Shuriken' before 'Lightning Rush).
I know my runes aren't that kind of useless for most of you, but I don't really need Magic Penetration, Cooldown Reduction, Health, so AP is the best for me, if you don't want to buy Void Staff, you might wanna buy Magic Penetration runes, because they will like forfeit the Void Staff.
Kennen is a Caster, that's why the 9-21, because of his Spell Penetration, and Health, reducing all damage dealt, due to the unnedless CoolDown reduction, mana re-gain, etc.
I don't think there are any other possible masteries for an AP Kennen, so I won't write anything, I will be posting my Hybrid/DPS later.
My items are pretty obvious for this little guy, he needs spell vamp after Mejai's for:
If needed, you can be a carry, because if they focus and you have your 'Lightning Rush' right after throwing a 'Thundering Shuriken', you activate 'Slicing Maelstrom', and if they focus, you will just drain 20% of ALL damage dealt to each champion, and you will be full-hp after stunning them with the 3 Marks Of Storm.
You can always regain some HP at the Wands, Dogs, Minions, and go righ back to fight.
I always raise 'Thundering Shuriken' to deal amazing damage still in lane phase, and at level 18, deal like 600 damage with an shuriken to the middle of them, and remove a big nack of their life.
Kennen can clear a complete wave of minions at lvl 12, but you can also do it on level 10 if you have already at least 18 stacks, it's a complete desvastation and healing if you already have Hextech Revolver.
Pros / Cons
Useless chapter, since I don't see any Consequence in Kennen with this build, you can perfectly do a 1vs1, so, I won't be posting anythin here.
Conclusion, you should give it a try! That's my advice, it's really fun to play with Kennen, because after Mastering it, you can't lose.