I am rather new to Teemo (about a week of 2-4 games a day), and am looking to get some user feedback on my build. I feel I do quite fine, just wanting to know if any experienced Teemo players have critiques or comments, please do, I would love to improve.

I chose to take heavy AP runes for the bonus magic dmg done on strike and the DoT tick on Toxic Shot, and the Attack speed runes for early harassment and easy multishots in early game

For Masteries I have found Teemo to be rather unique, so I gave him some defense to sustain better with health & hp regen/5, and resistances and the minion dmg return to keep harass on champs while ignoring and returning creep hits to tank creeps a little bit better.

I believe the items I have listed are the best items in combination. With the Nashors Tooth, giving a great bonus of Atk Spd +50% for layering initial dmg and tick dmg with Toxic Shot, and +25% Cooldown Reduction (for shrooming around, and running/blinding),The Malady allows for breaking down enemy magic resist, and gives a great speed boost, The Void Staff allows for great magic penetration, and The Rabadon's gives a great 140 AP(and the 30% AP boost), and the Lich's Bane gives an awesome burst in damage after the blind, while sustaining Toxic DoT ticks throughout the fights.

With the heavy AP boost with Toxic Shot, it is great for early game harass and carry through the lane, taking the Blind second will allow for better harass and allowing a heavy lane push while having to worry less about incoming damage, and instead of taking the run third, going back to the toxic shot will allow for better damage, and since you took the Boots of Speed first, the run isn't exactly a necessity.

I use heal, to sustain lane, and Teleport to port in on shrooms when allies are in trouble and need a Teemo rescue or even to recall out to regen at base/to buy items and port back in.
Another option I use, is Heal (again for the sustain), and Surge to lay heavy strikes and Toxic strikes.

With this build I have found that last hitting creeps is an easy and effective task for quick gold, and with the harass and carry, champ kills shouldn't be too far off on easy income.