You may be able to apply for a new work visa to extend your stay and work in New Zealand. Work visas may be granted for up to three years, but there is no limit on how many times you can apply for and get a new visa.  

Whether or not you’re eligible for a new visa will depend on the reason you were granted your initial visa (some categories have 'total' time restrictions), and whether you meet the application criteria when you apply for the new visa.