Oceania (Australia, New Zealand & the South Pacific) - Very semi- precious sketchbook left on a Jetstar flight

Hi!
I'm not sure if this is the right place to be posting something like this, but this site was recommended to me and I am needing to stretch all my options in order to find it.
It's somewhere with the airline Jetstar, between Australia and New Zealand. I have been calling relentlessly; however, I haven't gotten much useful advice from the people working for them.
I'm hoping by posting this thread, someone with the right connections can help me track it down as it is very important to me. It has a year's worth of work in in it and I just can't believe I won't see it again, I'm losing my mind over it.

Help please!!

What country was your destination? Saying "between" doesn't disclose which country you landed in. Also, what country are you located in? The process differs between NZ and Australia, also it is quite possible another pax picked up your notebook and then handed it in to the airport lost and found, not to the airline.

Contact phone numbers for JQ are at http://www.jetstar.com/au/en/contact-us#BaggageServices and differ by country.

But if JQ doesn't have it, then definitely try the arrival airport lost and found, also email customs there and maybe even try city police lost and found, in case it was turned in outside of the airport (e.g. try bus, train, etc.). I'd say chances are slim if the airline doesn't have it and they are normally very good about lost & found.