I found an iphone 4. Can I still use it?

It's unlocked and there's a kik app on it. Can I sign in to my account and use it?

You should find out who it belongs to and return it. That would be something really cool to do.

Just return it to the owner. Their name is in the SIM card.

Yes, you can use it. It'll work
The best thing to do would be to return it.
But whatever…

If ios 7 is on it then they can view where you are at all times because you can't remove their icloud account. They can also disable it.

Yea you could use it, but keep in mind that they can track the phone and know exactly where it is through GPS.

And once the owner reports the phone lost or stolen, it'll be blocked and can never be used by any carrier.

Just give the phone back, and save some one else a lot of trouble and money.