Teemo is a minion, why do I say that? Because the only thing minions do is push. And that's what you are going to do.

Well, not exactly. You're also going to secure objectives with your mushrooms, and you are not going to be left alone in a lane for long. You need to keep up vision, you have very high movement speed and people don't want to chase you because of your mushrooms. So you have the potential to never get caught, which makes teemo such a good splitpusher. Shroom and ward key points.

As for defensive runes such as armor and magic resistance, these are only to help you survive during the laning phase. Change them as you will. I sometimes run AS glyphs If I am facing someone who doesn't deal any magic damage.

Play super aggressive in lane, but don't trade! You don't have much sustain, you will be getting a scepter but it's not going to be enough to let you trade.

Since most tops are melee you should be able to kite them.
If they are ranged, use your Q and brushes. They wont chase into brushes after lvl 6, and pre lvl 6 you should be able to win most trades because of your Q+E. Also, if they retreat, use your W and get some extra attacks in there.

Be careful of the jungler! If you get stunned or slowed you die. (most of the time)

Keep up vision! Your prime concern is pushing, but unlike other champions, once you've destroyed the first tower, you continue further into enemy territory.

Use your teleport and chat system to secure dragon. If you see a fight building up middle, then immediately push to prevent it. That's what you do, you prevent 5v5s from happening because you are weak in those. And it will require a lot of skill to do this for 40minutes without failure, but it is possible.

5v5s around objectives aren't so bad since an engage is forced, but standoffs are Teemo's worst enemy. You are naturally squishie, you have low range and low nuke damage. Never attend one of these, there is always a lane to be pushed.

You have a very high clearing speed, you don't need crazy amounts of vision to be secure since you're near impossible to kill through lane and there are only 2-3 spots to get behind you. (which should be warded/shroomed as your progress)

So use your shrooms to clear waves too, it will speed it up which is crucial! speed!

Very few champions are able to take teemo 1v1. So if they send just 1 champion you should still be able to pressure the lane! It's amazing right?!

So your team is 4v4 which is fine, they should not get hurt too badly. But the key thing about splitpushing is not just forcing 4v4s, what you do is pressure a lane more then whoever they sent after you, so they will be forced to send several champions after you. Now you can either teleport to another lane, or just retreat. Either way, your team wins.

Now Teemo is weak in teamfights, so we ignore those....but we can't ignore objectives.

Place mushrooms at key points surrounding objectives and you should be able to provide more assistance than their top. Also early, with your teleport you will be able to fight 5v4 at dragon and it should be guaranteed. (Getting an early madreds is often viable, especially against AD tops, however don't forget your AS, your on hit damage from poison is very potent early on)

Now you just splitpush and secure objectives. Teemo has a high skillcap, and if you play him properly you can still make him viable.

This is also a very fun way to play if you ever get bored of the usual meta.

Remember to spam /laugh. I believe it is shift+4 but whatever...you'll figure it out.

You want them to focus you. You want that jungler to camp you! You will get your items since you are not dependent on teamfights.

If you feel like something should be added let me know. I have some replays available of good teemo games.

This playstyle has a very high skill ceiling, and if you play properly it will land you a high win percentage. I've tested it from 1600-1700 (teemo carried me up there lol)
About 15 games, but I take from others too, and a lot of theorycrafting. 75% winratio.

One game I went 3-12 and won...Another teammate had left because our odds to win were so low. But we won by sticking to our plan of splitpushing. Our team was behind 30 kills, and they had the ultimate teamfighting team.

However by securing objectives, keeping track of timers etc we managed to keep up in gold. And when the opportunity arose we managed to end the game. (It was 55 minutes of terror, everyone lost their lane, but we made it.)

Another game I lost my lane and went 23-3-10. Also by just sticking to my plan. Never giving up. However this game, the enemy would not give up their objectives easily, which was fine since they weren't the hardest champions to take down after walking through 4 of my mushrooms.

Goodluck out there summoner.