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:

Application.OpenURL ("fb://page/xxxxx");

The trick is to use fb:// instead… So far, so good.

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

So, I tried this one:

 void OpenFacebookPage ()
        WWW www = new WWW("fb://page/xxxxx");
    IEnumerator WaitForRequest(WWW www)
        yield return www;

        // check for errors
        if (www.error == null)
            Debug.Log("Sucess!: " + www.text);
            Debug.Log("WWW Error: "+ www.error + " Opening Safari...");
            //error. Open normal address
            Application.OpenURL ("");


But it did not work as I expected - always return error. I guess it did not work because WWW not support the facebook protocol.
In the Unity scripting reference:

Note: http://, https:// and file:// protocols are supported on iPhone. ftp:// protocol support is limited to anonymous downloads only. Other protocols are not supported.

So, I’m stucked here… Anyone knows how to solve this?

Thank you!

problem solved