WhatsApp uses the phone numbers saved in your phone's address book to find your friends who are already using WhatsApp. To learn more about why WhatsApp uses your phone number and address book, please read this article.
Follow these steps to chat with a friend over WhatsApp:
- Make sure that the person you are trying to contact has WhatsApp installed. WhatsApp can be downloaded from here.
- Ensure that you have their number saved in proper international format on your phone. You can find examples here.
- Inside of the app, go to the Favorites tab, press the button, and select Refresh Favorites.
Note: Sometimes numbers synced from Microsoft Exchange will not work in WhatsApp.
WhatsApp Support Team