Do you keep writing novels even if your novels only have 1 or 2 digit readers (or no readers - maybe you don't publish them)?
Public naturally arrives with time. For the first moment all you need is the will to write the story you want and build a good beginning.
But I personally work with the idea of prototypes. I post a concept first, something like 3 chapters or 5 chapters and try to build a good teaser. If the few readers who read it liked it I consider it a success.
If after a while it didin't work but I believe it could have potential I by myself would go after those readers. I'd change the cover, the summary, rewrite the chapters to be more interesting and work hard for new readers arrive.
If nothing works until the end of volume 1 (12-15 chapters) I consider it a failure and work with another concept.