free agent players are always three stars. so if you are, let's say, level 7, and you release a 4 stars youngster, then you cannot see him on your auction list. he will appear on level 8 managers' list. you can see free youngster if somebody in level 6 releases his 4 stars youngster. and considering that the period of generating academy players is long: 20+ days (that's almost one whole season), you cannot expect to find these youngsters so often.