"We have to work harder to change the culture, bring mental health to the forefront and erase the stigma that we can't talk about it. If you are suffering, call a friend or family today. We must save each other," she wrote.
In a follow-up tweet posted today, she apologised for referring to his death as a suicide.
Her updated tweets follow reports Genest's family do not believe his death was a suicide.
Fans of the fashion star feared he had committed suicide, but his manager Karim Leduc told TMZ Genest's family members believe his death was an accident.
Leduc said the model would lean against his railway balcony while smoking, which his family believe is what led to his fall.
They noted he had a creative personality and loved to write, saying it was strange that he did not leave a suicide note.
Leduc said Genest wasn't a drug user and was sober at the time of his death. He also said he had a "very positive mindset" and was working on several projects, including a new music video and a book of poetry.
Genest was known as "Zombie Boy" due to his distinctive tattoos and extreme body modifications.
As well as his starring appearance in the Lady Gaga video, the prolific artist — who had over 350,000 Instagram followers — booked frequent modelling jobs in magazines like Vanity Fair and GQ, as well as several small film roles.
iHeart reports that Genest is survived by parents Roch Genest and Catheryne Chappelle as well as two younger siblings.
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 police immediately on 111.
OR IF YOU NEED TO TALK TO SOMEONE ELSE:
• LIFELINE: 0800 543 354 (available 24/7)
• SUICIDE CRISIS HELPLINE: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• YOUTHLINE: 0800 376 633
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757