Sometimes tenants leave a property with rent owing and without giving notice. 
When this happens the tenancy is considered to be abandoned. 
The property is not abandoned if rent is still being paid.

If you have reason to believe your premises have been abandoned by your tenants, before entering the property you should apply to the Tenancy Tribunal in your state to have them declare it as abandoned.

Normally the landlord wants to get into the property as soon as possible to re-let it. While this is understandable, the law sets out a procedure that must be followed to protect both the tenant and landlord.

To support your claim you should provide sufficient evidence such as statements from witnesses, notices of disconnection of electricity, phone, photo showing a build up of mail and / or newspapers in letterbox etc.

If you are uncertain, and it is recommended in all circumstances that you are certain, you should obtain legal advice first or obtain an order from the Tribunal which will provide you with legal access.

With regard to any unpaid rent, the tenant is liable for the loss of rent payable and any reasonable costs of re-letting.