The family said they were relieved Joanna had been found but had no information about what had happened to her.
Her family said in a post on a Facebook page dedicated to the search that they hadn't been able to speak to her directly and she was with the Dutch police.
A Givealittle page created to support the family during the search, including flights to Amsterdam, accommodation and social media advertising, has been shut down.
The family are still going to fly to Amsterdam on Monday as initially planned to support Joanna.
Any remaining funds would be donated to charity. A police spokesperson said earlier that police were working with Dutch authorities through Interpol channels during the search for Joanna and were also offering support to her family in New Zealand.
Her sister Maria Ji told the Herald earlier this week that Joanna, a former University of Auckland law student, has been in Amsterdam since December on a working holiday visa.
"Usually she would message my mother every other day, but suddenly she just stopped from last week," Maria said.
"Then her handbag, wallet and mobile phone was found by a member of the public and turned in to the police there, so we know she doesn't have any of those belongings or money on her."
Maria described her sister as a creative, outgoing and bubbly person who was really empathetic and passionate about lots of social issues including human rights, animal rights and gender equality.