Hi Emily Charlotte,
Like others have said before, if you want a teaching job with a decent paycheck, good working conditions and career prospects, you need a TESOL/TEFL/CELTA cert and preferably one with a teaching practice component and not just online instructions and course work.
However, if you just wanna make a few bucks while "exploring and experiencing life" in Hong Kong while living here on a working holiday visa, you can get work at some language centers without a TESOL/TEFL/CELTA cert.
Why don't you apply to those language centers that cater to the Japanese expats living in Hong Kong? They'll value your experience teaching at an "Eikaiwa" in Japan.