I have had this happen a few times. Each time there were signs leading up to the abandonment. Such signs include rent arrears, and the tenant generally avoiding you. In the case of rent arrears, you should already have a tribunal application against the tenant for rent owing over 14 days. Keep this application going as you will need to apply again for vacated costs.
When your find the property abandoned, you will need to refer to section 61 of the RTA. With abandoned goods, you will need to get a second hand dealer to asses the items for their worth. If they are worth less then the cost to transport, store and sell them. Then the landlord may immediately dispose of them. Keep the secondhand dealers assessment on paper with photos of the items for your application against the tenant for vacated costs.
Arrange a skip bin and handyman to fill the skip and remove the rubbish. You’ll then need cleaning, do lawns and make repairs which usually include plumbing for blocked drains and electrical for light fittings. Also a handyman for general repairs. Take photos and an accurate report for evidence to support your claim for vacated costs at the tribunal.
If you are wise, and have REAL Landlord Insurance. You can make a claim for loss of rent due to abandonment. They could cover between 3 to 8 weeks depending on the tenancy.
Then the power account will need to be changed to your name so you can have power for cleaners. This can be changed over to the new tenant when they start, which will be about 2 to 3 weeks if the clean up is fast, and you can get good photos for marketing fairly quickly.
You will have 60 days to make your application against the tenant for vacate costs without needing their new address for service. So chase up all the invoices and get your application through to the tenancy tribunal.
Let the owner know what you are doing, they will appreciate your ability to make a potential disaster seem like a small bump in the road. These are great opportunities to build strong relationships with owners and get referral business. Every down-side has an up-side.