For a ganker build, i would run Teleport and Ghost, both for movement speed and the fact that teemo can use his w and ghost to get away quickly or get into position while teleport is on cooldown.

if you suspect crowd control in blind pick, Cleanse is a good idea.
Some may run heal, but the lifesteal from the bloodthirster should take care of that.

Pro: teemo can go invisible
Con: oracles or sight ward

Pro: High mobility
Con: crowd control

Pro: Teemo and his allies can teleport through his mushrooms
Con: shrooms can be destroyed by either tanking or attacking with oracles elixer equipped

Pro: Shrooms can help teemo escape
Con: wards

The reason i go 22/8/0 is because it gives teemo lifesteal at level one and no need to buy a dorans early game. Also, Magic pen is great because Ionic spark is magic damage AND Rylais Crystal Scepter causes ALL magic damage dealt to apply a slow.

Malady for magic pen, which procs with your masteries, Rylai's procs an effect similar to frozen mallet, but applies a slow in an AOE AND gives him more ability power. His poison hurts and he gains lifesteal from the frozen mallet. That being said, one can build an Infinity edge to substitute for the Black Cleaver, but that is entirely up to the player, but in that case i would recommend buying some Berserkers greaves to supplement the attack speed and thusly do more damage in a shorter amount of time.

Get E, Q, W and max the E until lvl 6, get your ult and continue maxing the remaining three abilities, and at 11 and 16, your shrooms.

Last hit and harass. This build works best for solo mid teemo, but don't be too aggressive, because your poison hurts and you know it.