The book I am writing has several characters in it all of whom are interesting, they are all part of an informal group they don't know each other particularly well although in the end some will get to know each other in ways they didn't expect. Is it always necessary to have a main character in order to build a story that people will read? Do readers demand that one of them be the main character?
I think there are published books that follow several characters without having one central person; War and Peace comes to mind.
The next thought that comes to mind is that War and Peace probably wouldn't be considered commercially publishable these days.
It's probably easier to keep a tight and pacey plot when following one character. If you have lots of strands that start out unconnected it will be more difficult to sustain a readers interest.
Brick Lane, for example, occasionally broke off to tell the story from the point of view of the main character's sister; this worked well because the novel had already devoted enough chapters to introduce us to the main character and the reader understood the connection between her and her sister's stories. Alentejo Blue, by the same author, didn't have the same strengths (in my opinion) as it flitted between too many characters.
Maybe one way to help you make your decision would be to write two outlines; one where you continue with several characters that have an equal share of the book's focus and another where you pick a central character that interacts with the rest.
Hope that helps.