My iphone got lost someone found it and they won't give it back?

Okay so yesterday i lost my phone because it fell out of my jacket without me knowing. I realized i had lost it a hour and a half later and i looked for it outside and didn't find it. I still didn't give up looking so i called it and yesterday it took me straight to voice mail because the battery had run out but today that i called it would ring and ring like it does when you don't answer and then it sends me to voice mail. All day i have been calling and the same thing happens until a couple of hours who ever has it turned off since it took me straight to voice mail. My dad Gpsd it and it lead us to a house that really close by. I was wondering if this is considered them stealing it since they clearly know we're looking for it and they won't answer. Should i get the cops involved?

Probably a good idea.

I'm a cop just give me your cell phone number and I'll talk to them about it.

I'd say approach the house, get cops involved if you want to. They could get charged with theft if found guilty. Definitely do something. Maybe text it and call it more and try on private mode #67 and your cell number

Go on iCloud and sign in with your Apple ID and password. Google this: "iCloud find iphone" click on the iCloud one. Click on your registered phone and lock it and put a message to display. Go to their house and ask for it back. If they refuse to give you your paid property back get a cop or something

Well if you had an email in case for backup or something and an app called find my iPhone you'll be ok and if you had a pass code so no one will get in your stuff