A dowser would not need the water to be running to find the pipe. But unless it is a metal pipe, a metal detector won't work. Plastic pipes have been used on farms for many decades.
If you know where your meter is and you know where the pipe enters the house, the tap must be somewhere between the two. Normally the installer will take the most direct route unless there is an obstruction that makes this impossible. I would start looking first near the meter. If it isn't there, look near the house.
If it all proves too difficult, it might just be easier to get someone to lay a new pipe. That, at least, will give you a guarantee of many years of leak-free service.