You can view your friend requests and your friend list on your profile.
For iOS: Go to My Profile > Tap the "^" arrow on your profile picture > Then scroll down to "View Friends".

For Android: Tap on the "..." in the top, right hand corner > My Profile > Tap the "^" arrow > Scroll down to "View Friends".

A list of friends will appear here with recent friend requests at the bottom of the page.
You can then select the profile of a friend you want to contact, tap the up arrow on their main profile picture and select Message to send them a message.