It depends a lot on where you are, and whether you knew the identity of the car. I once lost my phone in a private hire in the UK (these are essentially less t

It depends a lot on where you are, and whether you knew the identity of the car. I once lost my phone in a private hire in the UK (these are essentially less tightly regulated taxis that cannot pick people up off the street, they must be pre-booked only, and are what Uber operates as), and having emailed the office kept getting told that he was going to hand it in to the police as lost property "tomorrow" for a number of days. In the end, I told them that unless he handed it in within a further three days I would go to the police and make a complaint of theft against the driver, with all the emails between me and their office as evidence that a) they knew who the driver was even though they wouldn't tell me, and that b) he had it. Surprisingly enough, it got handed in within a couple of hours after that.