Originally from China, Sang says she comes from a rather conservative family background.
She is not lesbian or bi, but said she is aware of the bigotry out there and the challenges LGBTI young people faced.
"It may be legal for gay marriages, but as a society there is still little understanding and acceptance for LGBTI people," Sang said.
"Many young people hide their identity because they just don't know what reaction they will get from family and friends if they came out."
Sang is still in the process of looking for sponsors and judges for the competition, which she hopes to run in September.
"What allyship means to me" is the theme of the contest, which is aimed at promoting awareness about the presence of a youth LGBTIQ community here and show how critical allies are for them, she said.
"My hope is that through the submissions we receive, interested readers can develop a fuller understanding of how to be a good ally and how critical allies are for LGBTIQ youth," Sang said.
St Cuthbert's College Principal Justine Mahon said the school was unaware of the competition as it was something Sang and her friends had undertaken independently.
"However, I think it is a fantastic idea, and will be helpful in raising awareness about the importance of accepting people for who they are, and supporting each other over the establishment of their identity," Mahon said.
She said the school will publicise the competition and the essays themselves through its social media channels.
"St Cuthbert's is very supportive of all our girls and the establishment of their identity, and we do understand how very difficult and sensitive it can be for girls to come out and be open to their friends, family, and community about their sexuality," Mahon said.
"We encourage open and age appropriate discussions about sexuality, and our girls are educated and encouraged to understand that we are all unique, and to embrace diversity – whether it be ethnic, religious beliefs, or their sexuality."
At the school, LGBTI girls, their friends and supporters meet twice weekly, facilitated and supported by teachers.
"Our wrap around pastoral care approach to our girls ensures that if they need additional support or counselling, this is available," Mahon added.
According to the New Zealand Attitudes and Values study, about 2.6 per cent of New Zealanders identify as gay or lesbian, 1.8 per cent bisexual, 0.6 per cent bicurious, 0.5 per cent pansexual and 0.3 per cent asexual.