The Doctor didn't take long to look around York. After meeting Dawn and leaving the TARDIS near the Gates (mainly so it could recharge), he'd started exploring--away from all the super-powerful Gate energy.
He found the town's main drag easily, and started looking around at the shops and motels and restaurants. He knew, even before arriving, that people were missing from York. He also knew a lot of them weren't native--they were trying to help, like he did.
So the Phoenix Motel was a good place to start. And the dark haired girl outside was a good person to talk to, the Doctor reasoned.