Can't track anything

yes i mailed an letter to a friend of mine for mascot payments and i mailed the letter off 08/27/2014 and the expected delivery is saturday 08/30/14 and my tracking number is 911490118986674363689 and every time i track it on usps tracking it will not track it and i heard about usps tracking being down? but i need the tracking information for my tracking number here 911490118986674363689