Welcome to the party! Kennen support has been the only way to make the role fun against better(silver...) opponents. I would not play this in ranked without your adc being stacked with you, and even in norms it helps a ton.

Kennen is probably one of the most irreleveant champs if you dont play top or high elo mid(riot nerfs him before amumu lmao) but use this to your advantage. Your first ultimate is going to be a 100% free double if you stun both enemies and have someone to back you up. Like all off meta, use the lack of info to your advantage

The runes explained:
Elec: top tier kennen rune due to your ult and stun combo that proc it.
Taste of blood: less recalls, you can proc ToB on demand with your high q speed and range
Eyeball collection: subjective, go whatever suits you
Ultimate Hunter: only hunter you should ever go, your ult is half your damage.

Secondary:
Runes to Avoid: magical footwear, biscuit, POM, Shield Bash, and overgrowth.
Everything else is viable, find what suits you, my hyper aggro playstyle suits conq + last stand more.

Play passive pre lv 6. Always.ALWAYS, keep track of your w passive(im being a hypocrite but learn from my mistakes). Its the e***iest way to catch someone out. Just Q+W+AA and you are set. If you are going against someone with no hard cc, just e to them when possible. Flash from a bush to the enemy to get a free trade, kill, or flash out from them. E towards the adc randomly to scare the **** out of them and pop a flash. YOUR ULT GIVES YOUR RESISTANCES. Always remember that, you can absolutely destroy anyone trying to dive you, which in this meta, is a huge gamechanger(disclaimer, Zed does not count)

I cannot understate this. ROAM. Your E is one of the best roaming tools a support can have(beaten only by classic roam supports like bard or pyke) but you still do the type of damage as a lux or xerath. Make ur midlaner win lane every game, and then you yourself win the game. I always go boots first on this champ, unless I plan on staying in lane. Mobies is great at conserving energy but swifties works during your ult and e, so try both and see what you prefer.

Late game is where Kennen starts to really shine, your obscene ap ratios allow you to solo kill anyone that your are better than, even if you're down levels or items. A tip I have is to use your ult very aggro, like rocketbelt flash e into 3-5 enemies to stun, even if you die it will almost always net you an assist if you have your team with you. Another tip is to use your ult like a lockdown tool to prevent the enemies from escaping from an area, buying your team time.

If you went aery, you wont be doing as much damage late game, but you can still play off poke and cc like you did early.

Kennen is hard. I don't care if you see ranged top and think he's ap vayne, he is hard to master. Kennen support is one of the most skill expressive champs I have ever played, and its the most rewarding too. I lost most of my first few games, but I didn't give up, and eventually I do good every game. The 1 takeaway I want you to know from this guide is that play who you want, where you want. Some champs just don't work from the get go, but many champs just need a little reimagination of the playstyle or items. Have fun summoner.