Let me first tell you that this guide isn't an all exclusive, where I go in depth with how to play Teemo. I will, when I get the time, try to setup some graphics on how you can 'control' the map as Teemo, but that wouldn't be just yet.

I have no runes suggestions, basicly because I'm still working on figuring out what to take, as soon as I've figured that out, I will be making a chapter that explores the possibilities of which runes to take.

I personally love AP Teemo. Your Mushrooms becomes extremely reliable, and more importantly become a weapon against your opponents, instead of as AD Teemo, mainly only work as guards and protection. As AP Teemo your dmg is extremely well, if I may say, meaning pretty many AD Carriers will fear you and your blinding shot.

At last I'd like to announce that this isn't a big in-depth guide which explores AP Teemo completely, atleast not yet, and there may be some unanswered questions, which your more than welcome to ask in the comments below, but do keep in mind that this is my first guide.

For Masteries I went most Utility, and with a few points into Defense. I find Teemo quite squishy, and therefor I think it's needed to protect him better, by giving him a few more options to survive, when being encountered. My build works mainly with the summoner Spells Flash & Ghost, since thoose are the summoner spells I prefer, and later on in the guide, you will know why I prefer theese.

Giving Teemo more survivability, also makes Teemo more reliable, meaning he will less often have to retreat cause of low health, and since AP Teemo isn't too much depending on mana to make a great outcome, he will therefor be very usefull in longer fights.

As you can see I took Quickness to increase the movement of Teemo. My playstyle with Teemo, depends a lot on his movement speed. The moment speed are easily able to break up teams if they chase ya, aswell as your quick availability to pick up running champions.

This Chapter is as said not completely tried out yet, so I won't be making a bit speech about the current ones I have given this guide. All I can say is that at the current moment I am going for thoose runes because I feel they have the right combination of survivability while still giving Teemo more dmg.

If you have any suggestions, or already tried combination of runes for AP Teemo feel free to list in comments below. I'll take them into consideration and I love getting constructive criticism.

Now to the more sweet part, and hopefully the part I can actualy give good advice on. I've been testing a lot of different combos of items with AP Teemo, to find the exact right measure for playing AP Teemo.

First of all I'd like to list the items I prefer getting, and they are put in order in which one you buy first.
Doran's Shield - Berserker's Greaves - Malady - Rylai's Crystal Scepter - Rabadon's Deathcap - Lich Bane - Nashor's Tooth
This is the list I prefer taking. It has a good combination of Attack Speed and AP, with a cool slow and a decent additional dot.

Items that you may consider in case meeting a heavy armor team, stun combination team or anything else that resolve in less squishy targets for you to pick out easily.
Sorcerer's Shoes - Mainly because they can penetrate a high magic resistance team. I use them myself, if my team is a bit too much AP based.
Zhonya's Hourglass - Has an awesome Active, which is incredible if your being the target before others. I don't usually pick it, since the item I would trade with it is Lich Bane, and I prefer the Passive on Lich Bane, but I can't denie the fact that it's an awesome Active.
Hextech Gunblade- Simply because It's not too bad, I wouldn't usually pick it, but it increases your AD a bit aswell as AP, which can work cool against a team that has stacked their Magic Resistance.
Mejai's Soulstealer - Incredibly if you are able to get it to stack 20. The cooldown reduction works well for more blinding shot, and a bit more often Move Quick. The AP boost it gives is a lot valueable. But I still wouldn't consider taking it too often, since I feel your Attack Speed is very important, and giving up Malady or Nashar's Tooth for it, wouldn't be ideal, if you ask me.

I will be addind more items, as I research more on the subject.

At last I would like to say that I'm still updating the guide, and the current state it's in is not complete. So you perhaps will feel a need to know more, and that's understandable, but I'd need more research time to complete the guide.

Please to ask any questions regarding anything. I will gladly answer or edit my guide to make it more complete.

In advance I thank you for reading this and I apologize for any spelling faults.