THE family of a Melbourne woman missing in Croatia may sell their home in order to put up a six-figure reward for information on her whereabouts.

Britt Lapthorne, 21, was last seen in a nightclub in the Croatian coastal resort of Dubrovnik on September 17.

The RMIT student's brother Darren arrived in Dubrovnik on the weekend, and her father Dale plans to fly there on Friday.

The family, who says it is living its "worst nightmare" believes the hunt for Britt has been hampered by incompetence by Croatian authorities.

As well as creating a Facebook search page, Dale Lapthorne said posting a reward may be the only way to get people to provide information on Britt's whereabouts..

"I'm prepared to post a very large reward. I don't have the money, but I'm prepared to sell my house if I have to for our daughter," Mr Lapthorne said.

"I've been told it needs to be in the six figures, and I'm not talking Australian dollars, I'm talking Euros. We won't get people to talk otherwise."

He said there was "absolutely, definitely" people out there the Dubrovnik police are just not interviewing.

The family is pleased the investigation has finally stepped up a notch – after two weeks – with an Australian Federal Police (AFP) officer due to arrive in the city tomorrow and a homicide investigator from Zagreb on the scene.

"Time is of the essence, we haven't got time to waste. We know the Croatian authorities have been doing a pretty poor job until now," Mr Lapthorne said.

Prime Minister Kevin Rudd today said more AFP officers would be sent if needed and the Government was doing everything it could to help.

"... This is very hard, it's a different country, different culture, but we will not rest until we've put every effort into trying to track down this young one," he told the Nine Network.

"She's an Australian, she deserves every bit of consular assistance we can provide."

Mr Lapthorne said the family would not stop looking for their beloved daughter.

"I'm not going to go away. And I need the support of the Australian Government for a final resolution for this, hopefully not my daughter in a body bag but I want to bring my daughter home."

But he's realistic about the chances of her being found alive.

"I can't say I'm confident. At the moment I'm feeling ... she will be found. We're getting information, not from police, but from our own people ... that's getting us really close, really close, I'm confident of that.

"I'd be naive and stupid if I said she was definitely alive. In a case like this it's generally for the worst, but I'm living on that glimmer of hope and until I know otherwise we're not going to give it up."

Britt's bank accounts have not been touched, her passport and bags remained at the hostel where she was staying and the family said there was no chance she had just continued her travels.

An Australian parliamentary delegation, which includes Family First senator Steve Fielding, was currently in Croatia and had offered to help in any way they could, Mr Lapthorne said.

He's also thanked the public and the media for their "tremendous" support, saying without it the situation would be even harder.