Locket is intended to be used only with close friends, not strangers. In fact, there is no way for your teen to meet new people, discover new friends, or search for other users who they don't already know on the app.
Instead, friends on Locket can only be added from your phone's address book, by sharing your unique invite link, or by sharing your exact username. This helps ensure that everyone your teen adds on Locket is someone they already know and trust in real life.
Think of it like a phone number: only people you share it with can contact you. When talking with your teen about Locket, encourage them to only share their username and invite link with people they know and trust, just like their phone number.