Yes, instagram is a huge part of promotion. I’ve got many readers from others promoting my stories on their instagram, or from readers seeing my posts.
Also, what really helps is when you start a new story. My first story was shelved, gained a lot of reads and gave me 1000 new followers. So when I announced a new story I didn’t have to start from scratch. By day 4 I had 1000 which had previously taken me 3 months. Plus it’s a lot of fun interacting with your readers!!