As an unpublished author, we don’t have the profile that published authors have, at least, not yet.
It can be tempting to focus on the number of people and get discouraged when it’s not huge. One thing to remember here is that quality is better than quantity.
The first thing to do when you create your page is to invite people who are already your friends. Choose carefully the people you want to join your page. Not everyone will be interested in your writing journey, so choose wisely when sending invitations. You can also post a status update inviting your friends to join your new page.
If you are a member of any writing groups, let them know about your new page too. Before posting about it, check any rules they may have on the group about advertising and promotion. The same goes for any pages you visit.
Link to your page from your blog if you have one, and anywhere your supporters may see it, inviting them to join.
As you share your journey and your work, you will find that people will start sharing and joining your page, growing the numbers, and by the time your book is published, you will have a following of supporters on Facebook, all ready to purchase and promote it.
P.S. My page is here