One comment about your build:
As Teemo has no reliable slow, Phage/FM become super important on him. I'd suggest your build going something like this:
Last Whisper/BF Sword (Depending on whether or not you are forced back/killed more often and have to buy in parts, plus whether or not the enemy team has obvious armor stackers like Malphite/Rammus)
Other of Last Whisper/BF Sword
Vamp Scepter (keeps you from going back as much at this point)
Upgrade Vamp to Bloodthirster, Malady, Stark's, or Exec's, depending on circumstances (Exec's if they've got mundo/healers, Stark's if no one on your team has it, Bloodthirster if you have the money to get it in one go, Malady otherwise)
Upgrade Phage to FM
If game goes on, sell Doran's for Zeal, then up it to Phantom Dancer.