WhatsApp can find which of your friends are using the app quickly and easily. It reads your contacts' phone numbers from your phone's address book and automatically adds them to WhatsApp. Your contacts who have WhatsApp accounts will automatically appear in the favorites screen.
If you would like to add someone new to your favorites list in WhatsApp, simply enter their name and number into your Blackberry 10 address book.
When you add contacts to your address book make sure that you enter their phone number in full international format, especially if they live abroad. International format is:
+ [Country Code] [Full Phone Number]
Note: Remember to omit any leading 0's from the phone number.
For a detailed explanation on how to add international contacts, you can read more here.
To see your Favorites simply tap Favs at the bottom of the screen. Other ways to access this list are by tapping the 
Tab Menu or by swiping the screen to the right, and then tapping Favs.
To see your Contacts screen on WhatsApp simply open WhatsApp > Tab Menu > Contacts.
If you are having trouble adding contacts, please read this FAQ about WhatsApp and BlackBerry 10 contacts for additional information and troubleshooting tips.
Learn how to add a friend on: Android | iPhone | Windows Phone | Nokia S40 | BlackBerry | Nokia S60
Cheers,
WhatsApp Support Team