While there is no single established platform currently known as the "Giant Boy Zone Forum," this specific phrase often appears in niche communities related to giantism (macrophilia) or growth-based fan fiction.
The community has become wary of casual tourists, trolls, and content scrapers. As a result, active members often obscure the direct link, encouraging new users to discover it through handshake protocols—like joining a related Discord or Telegram group first.
If you simply want historical content (posts from 2015-2019), the Wayback Machine has snapshots of the forum at giantboyzone.net. While you cannot log in or post, you can read thousands of stories and view art. This is a safe way to preview the community before seeking the live link.
The forum you are looking for is most likely Giant in the Playground (often referred to as GiantITP), famous for its "The Order of the Stick" webcomic and tabletop RPG discussions. Quick Link Forum Home: Giant in the Playground Forums Key Sections