She had been involved in pulling 12 people out of the surf in a rescue at Huntington Beach in Los Angeles during a trip there in 2009, he said.
"She would risk her life. It didn't matter how big [the surf] was or the circumstances - she would go straight in."
He said Ms Hosking was relentlessly positive in the face of adversity and a key personality in the club.
"It's going to leave a big hole."
Friend Jaimi Bailey said Ms Hosking always had a smile on her face and was fun to be around.
She said the Piha club would not be the same without her.
"You had such a big heart and was always the person to go to when ever there was something wrong.
"You made such an impact on so many people and you will always be a strong part of our team. I am so lucky to call you my friend."
Martha McDonald said Ms Hosking was a great friend who she shared many good memories with.
"I am incredible sad that you are gone missy. You are such an amazing person, you always made me laugh and I will miss you like crazy."
Ms Hosking's body was still in France and her parents were investigating ways of bringing her back to New Zealand, Mr Brown said.
Piha Surf Life Saving Club was planning a tribute to Ms Hosking on August 27, he said.
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