Open facebook app instead safari / iOS - C#

I'm trying to call the oficial facebook App from my game instead open the safari browser. When the user click on my facebook button, I want to redirect him to my facebook page using the facebook oficial app.

I could using this:

The trick is to use fb:// instead http://www.facebook.com... So far, so good.

But what if the user does not have the facebook application installed?

So, I tried this one:

Open facebook app instead safari / iOS - C#