How do you change the text size in GUI.Box

The text I am using is really small. I need to get it bigger to be seen on a mobile phone.

function OnGUI ()
{
	GUI.Box (new Rect(Screen.width/2-sizeX/2, offSetY, sizeX, sizeY), "Score: " + currentScore);
	
	if(fading)
	{
		GUI.color.a = Mathf.Lerp(1.0, 0.0, fadeOut);
		GUI.DrawTexture(Rect(0,0,Screen.width, Screen.height), fadeTexture);
		
	}
	
	
}

It works great, I have tried several of the ways here, but they do not work on mobile. What am I doing wrong?

You need to use a GUIStyle. Here is an example :

var scoreStyle : GUIStyle = new GUIStyle("box");
scoreStyle.fontSize = FontSize;
GUI.Box (new Rect(Screen.width/2-sizeX/2, offSetY, sizeX, sizeY), "Score: " + currentScore, scoreStyle);

You can read more about GUI cusomization here : http://docs.unity3d.com/Manual/gui-Customization.html