One of my clients need a Friends Locator app, pretty much like LocaFinder (if you want to get a sense of it). Basically, the user will provide a phone number from a friend -> friend must also have the app installed and will receive a notification to add the user -> after acceptance, the user can see the friend's location on real time. Can be very useful for parents and logistic companies, for example. Users will have a trial period, after that they need to subscribe to keep using the app (there must be a payment service integration like PayPal or similar). If you look at LocaFinder you'll understand the user interface, just be aware of the subscription fee!