So here is my first guide, ADC Teemo. The Item build I posted is what I typically choose and is not exactly common for ADC, however in my experience it works. The Last whisper at the end is a situational item, I sometimes end with a wits end or second bloodthirster.

Madred's Bloodrazor is a good item for Teemo, even if the enemy team starts building armor to deal with the AD then you maintain damage output with the Bloodrazor
Frozen Mallet gives Teemo the extra health to stay in a fight and output valuable damage. Between Frozen Mallet and MoveQuick there should not be a single champ that you cant kite and harass until they die.
Bloodthirster gives Teemo yet more sustain for team fights while boosting is damage greatly
Black Cleaver is a must have item with this build. The attack speed, armor shredding, combined with the bloodrazor and bloodthirster (respectively) makes Black Cleaver an essential item.

Toxic Shot - Especially with the most recent buff to Toxic shot taking toxic shot gives that extra damage in an early confrontation with the opposing team, which is why I take it First, and max it first.

Move Quick - I take move quick second and max it second due to the speed boost. Move quick allows you to chase your feeling enemies and secure the kills that almost get away.

Blinding Dart - I level this last because although blind duration increases as it levels, at level 1 the blind still lasts for 1.5 seconds, which is even to turn the tables in a skirmish with the enemy ADC or, prevent that auto attack from putting you in the grave while on the run.

Teemo's doesn't have a hard built in escape. Move Quick combined with the slow from a shroom do provide an escape but it is not as simple as a Caitlyn net or Vayne tumble, that is why I take Flash rather than ghost on Teemo. Ignite combined with the Poison from Toxic Shot help secure the kill.