I'm not a big fan of playing Stitches tanky in SoloQ. He get's more viable as tank, if you play with a well coordinated team.
You can of course mix the builds to counteract the enemy team. You shouldn't change Tenderizer, Gorge, Fishing Hook or Bolt of the Storm. Everything else is own preference.

As Stitches you don't want to stay long in one place (of course if you're not holding strategic points at the moment). That means you should try to gank and interrupt people switching lanes, but be careful: Many champions can 1v1 you easily in the beginning. Choose your ganks depending on the CC/Damage your teammates provide to maximise your chances of a successful take-down.
If you're low on health go back to base or hit a fountain, there is no need to gank with half HP.

Hitting the Hooks can be frustating at first, but very rewarding once mastered. You can hit through most of the walls, but not enemy structures like walls, gates, forts or towers.
Getting the mapvision is another important point for every Stitches Player. If you can spot people at neutral camps and successfully hook them, you might get the camp and a kill.

If you're not ganking (which you should), you can do some of the camps (later) or push lanes. When pushing lanes you should try to tank the wave, which means you should stand in the center of it and hit creeps. Your passive will kill the wave now faster.
If you try to do the neutral camps, be careful. You are fairly squishy, before you get some more HP and can heal effectivly with your E.
But then again, if you have the choice of pushing or ganking, always choose the latter.

Coming soon! (Upvotes may sway me to complete this faster ;) )