Not Updated For Current Season
THE GOLDEN RULE
You may have noticed that my build is focused on staying alive, and if you have not noticed, you will because I repeat the rule over and over in this guide. STAY ALIVE. I have tank items to make you last longer. My sustain item heals you for all damage dealt. This build, and this play style can be summed up in one sentence, or one rule. SPLIT AND LIVE
The reason I did not put summoner spells is because I believe that choice is really dependent on your playstyle.
Reasons for items
Sunfire Cape is chosen for its tankiness and wave clear. Runaan's Hurricane is chose for attack speed and wave clear. Guinsoo's is chosen for all of it's stats. The Hextech Gunblade is chosen for the hybrid stats and sustain. You can replace Spirit Visage with any item you like, preferably something tanky, but I like it because it adds to the sustain. I chose Hextech Gunblade over Blade of the Ruined King for two reasons. It gives AP, and you can heal off your abilities, including the poison from your shrooms and e ability. You may have noticed that I am big on sustain, which can be seen in my items and masteries. I like to stay alive in lane, and the longer I am in lane, the more I get to harass.
I go hybrid because it throws your lane opponent off. They will assume you will go AP, which you will, but they will not expect you to buy a pick ax. Going hybrid makes your lane opponent spend gold on items they would not usually get, and if you harass correctly, they will not have much gold to spare. Overall, going hybrid will make counter-itemization a lot harder for your opponent. Now the the tank items, since people know that Teemo is generally very squishy, having tanky items will make you last a bit longer. Now, you are no full fledged tank by any means. You are killable, you can be bursted. Having these items buys you time to escape and let you wreak more havoc upon the enemies.
Start to splitpush, and if people attack you, you may be able to trade and still walk out alive. Play it like you play tryndamere, STAY ALIVE. In this stage, people like to group, that is your decision on whether your team can handle without you, and they cannot. Make your choices accordingly. If you do splitpush, which I recommend, it is imperative you use your shrooms wisely and effectively. You will need the vision to get away from enemies.
This is the stage in which Teemo falls off. However with this build, Teemo is useful for his splitpushing. This build gives you a bit of tank, and the sunfire cape helps with the pushing. Play safe, do not take risks unless you can afford to. Shrooming is vital for vision, especially in this stage. Try to place shrooms around baron if you can.
I know this is not an in depth guide. I do not think Teemo is a hard champion to learn and pick up. However, that does not mean he is easy to master. Teemo requires experience, patience, and a certain mindset that makes you immune to the guilt of playing this litte piece of.... Anyway, best of luck!