the directors of the company that owns the aircraft must make formal notification to the police and insurers that the aircraft has been stolen, period. Not to do that exposes the directors to the crime of "misprision of a felony"- you must report a presumed theft.
What happens afterwards is anyone's guess, but you must report suspected crime.
imho, if the aircraft ain't found - criminal offence.
imho it is found - civil case.
if you know that somebody knows where the aircraft is, but ain't tellin, you need a writ from the court freezing movement and putting the aircraft under the control of the court which means anyone who touches. it is in contempt of court.
....or, call your local bikies;(