This build is based around speed and harassment.
E and R is the bread and butter for most engagements. He has no burst abilities so the most reliable engage method for me was: While in W, Ghost, Youmuu's before hitting target. The bonus to his damage from the MS, coupled with Stormrazor makes his first hit hurt and will make most ADC's run. E to keep them engaged and stunned while getting some autos down to drop them to execution % finishing with R. Keep your Q in reserve to pull a runner or a new target. If you kill with your Ult it refreshes for quite a while, because of Nimbus Cloak you can very easily chase down a new target and get another kill. Unlike Darius ult, Pyke can hit EVERYONE if positioned properly. With this build, you can easily get your pentas.

His jungle is weak early. It's why most people keep him support. But with a couple items it catches up quick. He can't build health so he has to heal for any chance of sustain. I start Machete for the initial healing but immediately build Vampiric Scepter for early sustain, setting up for Tiamat. Once you make Dagger and Brawlers, you can sell Refillable Potion and put it into finishing your RH. Start Red for healing and damage, scuttle, raptors then Blue scuttle if available, then Blue. Future Market will let you build quick. I wait for level 3 before ganking as you will need your Q to be effective. Getting W second lets you get around quick enough without boots and sets you up for more escape / catch options. Always W across lanes to keep enemies in the dark about your location, you can use items while in W so may as well ward a bush while passing through.

Futures Market lets you build quickly which is important for this build. First complete item is Ravenous Hydra because you can't build health. You need the healing early. After 10min build Boots of Swiftness for the added MS and slows reduction. Dagger and Brawlers set you up for Stormrazor and Phantom Dancer but lets you sell Potion as it's plenty to keep you up. Make Skirmisher Saber but leave Warrior mod until later, instead keep trucking on Stormrazor. Serrated Dirk sets up for Youmuu's or Duskblade. Depending how the game goes I trade out Youmuu's for Duskblade. But that's only if there is a late lane phase, Stormrazor should be enough to get through. I would work in other things like Deadmans Plate or Spirit Visage if resistances are a must. But this build is working as a hit and run assassin that can traverse the map quickly and support any lane.