First of all, under HK company law, we have private limited company and public limited company. I presume in your case it is a private limited company. Then there must have a document "Articles of Association 章程". We have to refer to this AoA.
1. Assume your AoA is a typical one. If you want to withdraw from the company, it means you do not want to be the shareholder of the company anymore. Usually the AoA will stipulate the existing shareholders have pre-emptive right in buying your shares. If they do not exercise the right, then you may sell your shares to third party under the same terms and conditions. Such share transfer will not require the approval of shareholders.
2. Assume your AoA is a typical one. A shareholder can also be a director of the company. In fact, it is very common in small private company. By law, the directors are appointed by the shareholders in the shareholder's general meeting. That mean they may appoint themselves as directors to take control and management of the company.