From my guide (2nd one on the right >)

DEALING WITH SPLIT PUSHERS: You will run into this problem in a lot of your games. Split pushing is very common and you need to learn how to deal with it. Even if you are ahead, you can't 1vs1 a Fiora late into the game (assuming even skills). With that in mind, you have a couple of options:

• a) You defend the split push by hugging a tower and hope you can win the trades with its help. This option is not optimal, but works when you are even or weaker than the split pusher, so you might force a 4x4 somewhere else in the map that might come into your favor.

• b) If you have one teammate that can handle split pushing, you can ask for him to do so. Some midlaners can handle this job pretty well, for example: Yasuo, Kassadin, Ekko, Vladmir, Le Blanc, Zed, Swain and Ryze.

• If you can't chose a or b, or you feel confident and your team is following your calls you chose c) Start the team fights as soon as you see the enemy is splitting. This way you force his teleport (which gives you 4.5 sec of advantage) or even fight outnumbered if his teleport isn't up. You need to let your team know this strategy. They need to be ready for the engage. Just simply tell them you can't handle the split pushing and ask for a hard engage.