"Loved by all his friends and family," the notice read.
Keast worked in the kitchens at The Stables restaurant in Matakana, and his employees this week paid tribute to him, saying he will be greatly missed.
"Thank you for all of you messages of support," the restaurant said in a Facebook post, which included a photograph of Keast in his chef whites, smiling while preparing food.
"Jethro was not only a valuable member of our team ... he was part of the place, he was our friend, and we will surely miss him every day."
Commenting on the post, Louisa Perkins said it was "so incredibly sad to not see Jethro over the pass ... no words".
Friends have also spoken of their loss on Facebook.
Jordan Tudman said he had "some great memories" with Keast.
"You were the first person to teach me how to drive manual, and even helped me buy my first car," he said.
"Rest easy my bro, you will be missed."
Another friend Connor Beehre said the news of Keast's death came as "such a shock".
"Never been so gutted in my life," he said. "Will miss you Jethro."
Deane Hornsby described Keast as a "beautiful soul".
Cameron Taylor said he had been "reflecting on how great a man the dude was".
A service celebrating Keast's life will be held at The Stables, Matakana, on Tuesday, followed by a private cremation.