Facebook brings new poke experience on mobile platform . It is now available only on iTunes. Check it out. Here is the link. Facebook Poke.
With the Poke app, you can poke or send a message, photo, or video to Facebook friends to share what you're up to in a lightweight way. You can poke an individual friend or several at once. Each message expires after a specific time you've set, either 1, 3, 5 or 10 seconds. When time runs out, the message disappears from the app.To see a message from a friend, press and hold the message until it expires.