NZRL high performance general manager Tony Kemp said it was a sad day for the sport and offered condolences on behalf of the national organisation to Fotuaika's family.
Kemp was sure the 20-year-old had the goods to reach the top.
"He got player of the day last year in the NYC (National Youth Competition) final, so he was on track,'' he said.
"Most of our national team now have been Junior Kiwis and Mosese was a Junior Kiwi last year, so he had plenty of potential.''
Kemp said he had no further details about Fotuaika's death apart from what was in the media, but said mental health was one area that New Zealand sport needed to spend more time on.
The Wests Tigers' official Facebook site posted notice of the loss while players such as Tim Moltzen and Aaron Woods offered their condolences on Twitter.
Fotuaika attended Keebra Park High, the same school as Tigers playmaker Benji Marshall.
- AAP