Good guide,it helped me a lot in bot matches.

and could you specify the 'something else' to replace nashor's tooth?

Its true he will do badly against an adc but the point of this teemo is to farm top lane to get fed mid to late. He needs cdr so he can put alot of mush. The whole point of this guide is to fill top with mush and farm as much as possible. Since you will be most of the time pushing to plant mush, if the adc top harasses you, he will get targeted by all the gathered minions and might not even win the trade. If it is a tanky bruiser teemo can kite him anyway with his movespeed. Teleport is because as I said to help him have more time farming. You will only go back when you run out of mana and that takes less time if you build a nashor's which has other stats that teemo needs too. Teemo is squishy, yes but if played properly he can take barely any damage 1v1 while dishing out alot, at least for an ad based champ.
If there is anything else you are not satisfied with please tell me as I believe it will help me improve. Thanks for commenting :)

also i would go with flash and probably exhaust for summoner spells... unless you want to be a pro in team fights. then flash and surge. Teleport isn't really needed much for teemo because he has a high passive movement speed anyways. Exhaust can really help you do lots of damage fast... Since teemo is so squishy also it will win you those 1v1 fights as you mentioned. Otherwise if you are laning against a ranged adc you might have a tough time. And ghost isnt needed either... he should just flash the use "W" to run away.

Nashor's may not be the best choose for an AP/AS item as it has CD reduction... teemo has relatively low CD and that is just one passive that could be replaced by something else. Also he isnt great at harassing because he has low range for a ranged dps so unless you are playing defensively against rather aggressive opponents, harassment will be difficult. And if the person playing teemo runs up to harass and shoot, all it takes is an exhaust and a couple hits to take out a teemo. Overall though it's not a bad guide. Just maybe a few ideas for edits if that's ok.

What you need is not magic damage or any more magic resist. You need that magic pen, without it you have only around 10% magic pen from masteries and those enemies just build a little and your madred's and any other form of damage other than AD will not be as significant. You can get your enough magic resist through banshee's which even block 1 more spell. What you need more is damage and in this case magic pen would work better than just more pure magic damage.

Wits End is better than Malady.

and btw its not AP Teemo, its a hybrid AS

Early on you can out harass your enemy and zone them easily. With your mushrooms no one can even gank you. Mid game you can be really strong if you can pull out a malady and parts of a nashor's. Just try it, it'll work out.

The problem is that if it can't do anything good in mid it won't do jack against any decent top player, AP Teemo doesn't even work top in the first place it's just annoying.