So I was doing that silver shroud quest, where you have to take out SinJin in the Milton General Hospital. And after I did it and left Piper wasn't behind me, she didn't follow me out the door. So then I went to one of my other companions and selected to have Piper head the the Red Rocket Cafe.

Well she never showed up. I waited and went back to search for her. Couldn't find her. Its really annoying. She has alot of good stuff on her.

Does anyone know what I can do to find her? I'm playing on a PS4 so I can't do any console commands.

The most common reason this happens is if you have an active quest involving the companion. If you do, they'll head to the next quest location, the same as if you'd told them you'd meet them there instead of letting them travel with you.

It wasn't a question related to her. It was just the Silver Shroud side quest. I did look for her in Good neighbor but she wasn't there.

American Badger is correct, it appears that certain companions are automatically moved to certain locations for that sake of an upcoming quest. I've experienced the same thing with Piper, without spoiling; she reappeared in Diamond City.

I had this with Nick Valentine: he was right behind me, I entered a door to an inside area and he was gone. I went back out and looked around and around and could not find him. Finally I went back inside and it turns out he had immediately moved farther inside to the quest NPC we were supposed to talk to, instead of following me from the doorway.

Later, I lost Nick because I had jumped off a bridge and then ran quite a bit before I remembered the A.I. doesn't like to jump. I waited and waited and ran back looking for him and could not find him, so I eventually used console commands to ~bring~ him to me. No help for a console player, unfortunately (just have to keep an eye on your following companions).

Check every NPC in the area and even the ones that ended the quest. She just vanished.

Honestly Bethesda needs to make a thing that shows you on your map where your companions are.

Or better still a pager that just summons them to you if they're beyond visual range.