Liandry's anguish: this item gives your shrooms much more damage and gives you a nice powerspike.

Sorcerer's shoes: these are must to buy as Teemo support or any champ with AP build.

Demonic embrace: this item makes your shrooms do percentage of the target's max health as a bonus damage.

Void staff: this item gives you magic penetration so your shrooms do nearly all the damage they should.

Rabadon's deathcap: this item gives you just so much AP that it is always worth it with an AP champion.

Horizon focus: this item makes your shrooms' and item passive burns 10% more damage. It also gives you 115 AP so I think it is a very good option for last item. Someone build nashor's tooth indeed and it is very good option too.

I first tried Teemo support as a meme pick, but then I found out it is a very good support with high damage and game impact. It gives your team so much map control too (especially if you take spellthiefs for your starter. I played it sometimes with just full AP but it didn't work really well. Then I found the perfect playstyle for it. Now I surprise people with my hyper-aggro bush camping Teemo support. The playstyle is so unique I have to make this guide little bit longer than I first thought. When you have read this, you have fully learned how to play Teemo support. Together we will make it meta.

Dark harvest: this rune is the best keystone for Teemo. It makes your playstyle feel more rewarding and works well with your role. I see no other option here.

Sudden impact: this rune gives you more damage when you leave a brush (and you will do that often) so it is the best option here. Some people prefer cheap shot but it is not as good as this.

Eyeball collection: this is the best rune on here, but it is not very good. It works on Teemo in late game but doesn't give much on the early game. Still it is a good option (and the only one here).

Ultimate hunter: this rune makes you have your shrooms more often so this is good for Teemo. Some people might prefer ravenous hunter, but I think support doesn't need life steal or omnivamp.

Absolute focus: absolute focus works well with your playstyle in late game because then you should be over 70% of your max health nearly always. This is (as nearly every rune in this build) a late game rune and doesn't bring much in early game. Transcendence is also nice rune for Teemo but I think it doesn't bring you game impact you should have, so I choose absolute focus.

Gathering storm: you are a very good late game champion and this is an optimal late game rune. This has given you up to 100 AP in 40 min. I always take this, there is nothing that can be even compared to this.

Pros:
+high game impact
+fun to play
+easy to learn
+deals tons of AP
+very good map control
+passive works well with this build/playstyle

Cons:
-bad in teamfights
-squishy
-useless if far behind

This is the most important thing with Teemo support. If you just play like the build says you will get 5-6 dark harvest stacks when the turret plating falls. But if you read this, you will get 6-8 stacks indeed. And of you have Tristana adc, you will have 8-10 stacks. So, as you can see, this is very useful knowledge as this is everything I could tell you about your playstyle and laning.

Starting items:
I have tried to get starter item recommendation for every matchup, but if they are different (spellthiefs by the adc and doran's shield by the support) you have to think about your adc, jungler and ability order. If your adc is passive pre-lv6, you should play safe too. If adc is aggressive, you should buy spellthiefs and camp bushes. Doran's shield is for passive lanes and spellthiefs for aggressive ones. Jungler is not the main thing to choose your starter item bit you can think about it. If your jungler is a bot lane ganker (blue Kayn for example) you can think about buying spellthiefs. If he is not, it's a point for doran's shield. Your ability order depends on matchup but it can be a really nice starter item recommendater. If you upgrade blinding dart first for a passive lane doran's shield is better but if you take it for bush camping or aggressive lane spellthiefs is better.

Helping your jungler:
Teemo is pretty good with junglers, because he can help them so much. At the start of the game you can go to river and watch out for the enemy team invade. Teemo's passive makes this a lot easier, because he can be just a living ward on the river. If you upgrade blinding dart first, please use one as a leash to the buff you are helping him with. Blinding dart's duration is doubled against jungle monsters. When the jungler comes to get the bottom side scuttle, you can help him. Go to the middle of the river and go invicible with your passive. You can be a living ward and of the enemy jungler comes, you can just blind them. You do little more damage because of sudden impact so the enemy jungler probably just runs away.

Playstyle:
This is the thing that makes my Teemo support so special. Your playstyle is completely different compared to any other support. You can't be seen by wards (except control wards) so you can hide on bush freely. Nobody can see you so you are safe and you can just wait for the right moment. If you choose to camp bushes, you have to buy spellthiefs because doran's shield is useless then. If you kill minions with doran's shield's passive, enemies see you and you are not safe anymore. But if you choose to play safe and behind minions, doran's shield is better for you. If you camp bushes, you have to know when to come out. Right time is when enemies are near enough to blind and below 75% of their max health to get a dark harvest stack. You can just surprise them with coming out of bush and immediately blinding them. With this tactic you will get the most dark harvest stacks and champion damage. Remember that you can get a dark harvest stack by just hitting an enemy below 50% of their max health.

Thanks for reading, I didn't believe you would read this far :)
If you have anything to ask or something to say just leave a comment. I will answer as soon as possible. If you liked the guide or the build or found it useful, please upvote this guide because it means so much to me. This is my first Mobafire guide ever (as you can see) but I think it's a pretty good one. I will update this guide whenever I find out something new or just want to make this better. I will probably update the graphics pretty much because this is just the first version of this guide. If you want to help me with them, just leave a comment.

Also, have great time with your hyper-aggro bush camping Teemo support and make enemies ff 15 :)