Facebook ‘Poke’ is a popular way to quickly say "Hi!" to a friend on Facebook. While the feature is easily available on the full-fledged website, the same is not the true when it comes to using it on a smartphone. You can ‘Poke’ only the friends whom you are connected with.
To 'Poke' a friend, on Facebook click on the symbol on the top left corner and type the friend's name in the search field. Tap on their name to go on their profile page. Now click on the ‘More Options’ icon on the top right corner. Here, you'll find the ‘Poke’ option along with additional options like ‘Call’, ‘Text’ and ‘SMS’. You can view the received ‘Pokes’ in the notification on the left hand corner and reply to them from here. Apart from this, you can even download the Facebook Poke app from the App Store. However, its usage is restricted only to friends who use an iOS device.