Willis, who played five rugby tests for New Zealand, was puzzled when told his jersey had been targeted over those of other prominent old boys.
''Why would they take mine? There was [Ben] Smith's, [Brendon] McCullum's and [Carl] Hayman's.''
He was disappointed by the theft and hoped the jersey would be returned.
Willis, who played for Otago, Waikato, Highlanders and the Chiefs before playing overseas, had a message for the thief: ''Just hand it back in anonymously would be a good start.''
King's High School rector Dan Reddiex said the jersey had a ''heck of a lot of value to us''.
''It is a special piece of memorabilia that Tom gave directly to the school because he was proud of it and so were we. ''And we would like it returned.''
Supervisor Rick Bourne, of the Southern District police investigations support unit, said the thief used a cloth to protect their hand before smashing a glass case and taking the jersey at the weekend.
Anyone with information is urged to contact Dunedin Police on 471 4800, or anonymously through Crimestoppers on 0800 555 111.
