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Their comments come after his family launched a Givealittle page in a bid to raise funds to bring Karika's body home.
The 31-year-old was described as having a "charismatic soul" with the best chuckle and one-liners.
Lily McManus said she was absolutely gutted by Karika's death, saying he brought such a warm, bright and charismatic soul to the Bachelorette show.
"He left such as mark on everyone involved. I hope he and his family are able to find their peace."
Lesina Nakhid-Schuster said he was a hilarious man with the best chuckle and the best one-liners.
"I loved hearing how enthusiastic he was about looking after his mum, learning about his gym and food routines, and creating funny handshakes together.
"I also really admired him opening the doors on the topic of mental health and some of his hardest times."
Nakhid-Schuster said her heart went out to his family and after having had the pleasure of meeting him she knew what a truly devastating loss this was.
"Rest in peace Tavita."
Karika who was a contestant in the Bachelorette NZ last year, is understood to have died around midnight on Thursday in Wellington.
He worked as an actor, model and personal trainer in Wellington and had also been training to be a barber. He is originally from Christchurch.
A family spokesman on the fundraising page described it as a difficult time for those close to Karika.
"If you had the pleasure of knowing Tavita, you will know just how difficult this is for his family, friends and all who loved him.
"We are wanting to raise as much as we can to help Tavita's family with funeral costs and getting our boy home."
Many of those donating shared their personal memories of a good friend. Others shared disbelief at the news.
Childhood friend Debra wrote: "Absolutely devastated to hear of Tavita's passing. Known him since I was 6. Used to give me piggyback rides home from school.
"Such a huge loss. Sending all my love to the whānau."
Where to get help
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call 111.
Stay encouraged. If you need to talk to someone, the following free helplines operate 24/7:
DEPRESSION HELPLINE 0800 111 757
LIFELINE 0800 543 354
NEED TO TALK? Call or text 1737
SAMARITANS 0800 726 666
YOUTHLINE 0800 376 633 or text 234