Welcome and thanks for checking out my guide to teemo. First and foremost this guide is meant for aggressive moderate to veteran teemo players, it focus's more on getting kills through sheer attack speed and attack damage by moving around the battlefield very fast and staying un-noticed. I usually go 7/0/7 or 7/0/8 before the enemy team surrenders ^_^
I am aware this kind may appear quite bare, if it reaches a point where people think it's useful I will add my tips on how to play teemo properly with this build on a step to step basis, and break item buying down according to your enemy champs and their play styles. Thanks for looking!

I won't go much into runes because honestly I believe they are based on each individual players, I personally focus on attack speed and ad/ap pen. I do a lot of surprise auto attacking early game to secure a head start on the opposing team. That's where the extra attack speed comes into play, combined with your passive and the possible addition of surge, you can easily take out an enemy champ at level one with ease.

The masteries tie directly into my runes, attack speed, penetration, and over adding to my burst damage capability early game.

As far as boots go I start for extra speed to last me considering I choose my W a little later than other builds, this gives me more room to upgrade my damage abilities and lay the hurt down early game, use your passive, it's there for a reason, get kills early and let the gold flow in. Malady adds more punch to your E and together with greaves and phantom you will have more than enough attack speed, any carry ad character should have a blood thirster, it's easy to farm it with teemo, just buy it go farm it with your high attack speed and it will increase your damage out put ten fold. Frozen mallet not only gives you health and allows you to slow enemies to continue punishing them as they try to run from your surprise attacks it works well in team fights allowing your team to attack the enemy team running by hitting all enemy champs over and over, keep switching to keep all their movement down while you and your team punish them. Most people don't think to build crit on teemo but when you hit as many times as he does you have more and more chances to proc it, so infitiy edge is just an excellent choice to boost your ad, your cs damage, and your cs chance. All these come together to make teemo a great assassin. And team fighting beast from the back of the line.