The thing about the Teemo-Darius matchup is that, in my opinion to a degree it's a skill matchup, because they're both considered lane bullies. Whoever out-bullies the other wins.
You have to understand that Teemo's strongest point is the first three levels, when you really feel his poison. As the game goes on Darius gets more and more tanky to a point where he can really just all-in Teemo whenever he can catch him. This is exactly why every single time I'm in this matchup as Teemo, the first thing I rush is swifties and I max W second over Q. Once it's post-3, my goal in that matchup is to be annoying and kite you without getting caught.
No offense, but it does sound like you aren't facing the greatest Teemo's. Ideally if they're in pull range, they should have thrown out the blind before you even began pulling, because the range is about the same and that's how they save themself from your W and thus get away.
In a 1v1, no jungler situation, Teemo's win condition is to bait out your pull without getting caught by it. This gives him a huge opening to start wailing on you and try to shove you out of lane. Combining the movespeed build with these factors is how Teemo wins: If you can't catch him, you can't kill him. This is why Teemo is considered a counter to Darius.
Similarly, this is also why if I play Darius into this matchup, I take flash over ghost: If you can get Teemo afraid of the flash-pull, you can zone him hard enough that he can't cs whatsoever. Don't even bother actually using the flash-pull, because then the lack of flash will make him less scared when he's back. Just knowing that you can do it to him is usually enough to keep him away.
In most cases if Darius survives to level 6, he's 'won' lane, because he scales much better than Teemo does itemless, so he can pull back easily at that point. That said, watch for shroom baits, because he can turn that nasty on you.
Now, if we were to account for junglers, then the matchup basically becomes a question of which one is more inclined to gank top, because Teemo and Darius both are very weak to ganks. Darius has no escapes and, while Teemo has his W and shrooms, he's also the absolute squishiest toplaner. If the jungler does manage to catch either of them, 9/10 times they're dead.
TL;DR: If the Teemo isn't braindead at kiting he can win, if the Darius isn't braindead about his pulls he can win. This matchup is big on zoning. Smart junglers can very easily decide who wins this matchup.
P.S. I play them both about evenly :P Lately I've been doing more Darius than Teemo actually, because in current meta Teemo is kinda garbage.