My friend lost his smartphone, and we're trying to figure out if there's a chance we can find it. There are many services online that offer phone tracking by number, but it's not entirely clear how they work.
Are there any truly effective ways to locate a phone by number, how accurate are they, and do I need to install an app on the phone itself beforehand?

Determining the exact location of a device simply by its phone number without the phone itself is virtually impossible. Carriers and intelligence agencies can do this, but such tools are unavailable to ordinary users. However, if we're talking about third-party solutions, consider services like GEOfinder mobile number location tracker. This app is often used in such cases. A person receives a message, opens it, and then can see their geolocation.

The only truly effective options are features like "Find My Device," but they must be enabled in advance. Alternatively, you can use dedicated tracking apps that are installed on your phone before it's lost and linked to your account.