Yes, you require an employment visa. The employment visa allows you to enter and stay in Hong Kong legally as an employee. It demonstrates that you have special qualifications, skills, and your stay will be of great help to Hong Kong. Apart from employment visa, there are exceptions when you are eligible to seek gainful employment.
Family members and children below the age of 18 years can enter Hong Kong using dependant visa that also allows them to seek gainful employment. The dependant visa allows the holder to work in Hong Kong for a period two years before seeking renewal for another two years.