Hi
@Arabic calligraphy – sounds interesting! I am not actually running a forum, so I don't now how valuable my advice is.
But I was one of the first members of this forum, and have seen its developement from a very small to a quite big community. I remember that Erica started by creating a lot of inviting content, like a welcome post, a post about how she got in calligraphy, a post encouraging people to say hello and tell a bit about themselves and their motivations, a post with a bit of information for beginners … you get the idea. Newbies that are maybe interested will not post with questions if there is no content at all.
The more content you have, the better you will be found on search engines too. Find out more about search engine optimization.
Also I think you could personally invite all the calligraphers you know already via a newsletter or similar.
I would create an Instagram and maybe Facebook or other social media account (I don't like FB, but that's a personal thing, so I can't say a lot about that) dedicated to the forum. Use fitting hashtags, so that people can find you. Post something interesting every few days and connect with other Arabic calligraphers via liking and commenting
.
Good luck with your forum!