Gold and Platinum FFs have access to more economy class award seats. But this is not the case for business class and first class awards.
Being Platinum may mean they will release award seats of none exist, but there is no promise or guarantee of that. I have had this happen twice - first time was in 1999 where I wanted 2 business class award seats to London and only 1 seat was available on the return leg and they released a second for me. The second time was when I wanted 2 business class awards to Singapore for Mrs NM and Mini-NM#1. I was on a paid business class flight and of course we wanted to travel togther on the same flight. I could only route them via SYD while my paid flight was the non-stop service. Again, a request for seats to be released was upheld. That was in 2000, so things may be different now.