Welcome everyone, hope I can help you a little bit with getting to know the wonderful champion called Teemo. I have a small youtube channel, and a few people suggested that I write a guide for Teemo. If you want to watch me playing, and learn by watching here is the channel:
https://www.youtube.com/channel/UCA1je34wYaqLV_eDsore7SQ

If you are up against AP champion go for:
AD marks
Scaling Health seals
Magic Resist Glyphs
AS Quints,

If you are at lower elos (gold or below) you should go Ignite to win the lane(against Pantheon I would still take TP), however after I got to gold 1-2 and now plat 3-4 I tend to take TP. The jungler usually ganks me at lvl 2 or 3, and if I die, or get to low HP I must go back, and without teleport, I would get behind really fast.

Your teamfighting potential is low, hurricane helps it a bit but you are still kinda useless in big fights unless you are fed. Unless your team has a great teamfight comp you should focus on split pushing, taking turrets, winning 1v1 , 1v2 fights.

If you are uncertain whether you can win your lane or not I recommend you to do not push your lane early on, and try to freeze it at your tower. It can be really annoying for your oponent, since he will have to walk up to you to farm, while you can harass him and your jungler can come and kill him, while his jungler can't gank you (unless they decide to tower dive). However if your team is losing and you are winning the lane, pushing can be really effective, becouse you will draw the jungler's attention from your team, and he will try to gank you, and if you can evade the gank your team might be able to win a 3v2 bot/take dragon/kill mid lane etc. Of course if you die to the jungler ganking you, it's a bad strategy, so be sure to ward and put shrooms.

Lower Elo: you should play agressively (unless you are counter picked) try to make the enemy laner fall behind, you should also look for towers, while your team is feeding bot, you should be taking the towers on top, you can't help bot even if you have TP, so just look for drawing the attention of the enemy jungler on you, and winning the lane. Getting a good jungler as a premade can boost your performance really well, if you check out my channel you will notice that I play with the same guy most of the times, he also uploads jungler videos, so if you are interested check it out.
High Elo: The enemies will try to shut you down, especially if you have ignite, the jungler will gank you early (LVL 2-3 most of the times) so you should not push the lane IMO. You can even ask your jungler to come counter gank at lvl 3.

Teemo is very versatile, you can buy almost anything and be OK with it. Tanky teemo is good if you are behind and need front line, AP teemo is good if your team lacks magic dmg,attack speed if you wan't to go split push, or you already have AP mid and don't need another full AP champ. This is why I love Teemo. I almost never build the same way, and you shouldn't copy my build 100%. Always adapt to the game you are in. If you build teemo the samne way in your last 10 matches you are probably doing it wrong.

I hope I could help you, feedback on the guide would be amazing, It still needs improvement, If you have any questions ask, I will do my best to give you a good answer. Hopefully your Teemo will improve after going through this guide, don't forget that you need to adapt to your game, and not copying my build all the time. After getting used to this build and Teemo in general, platinum shouldn't be too easy. GL&HF