Well, actually, the theme really has very little to do with this issue, and there’s certainly nothing wrong with the one you are using. The very most important thing is good, frequent, content. It also just takes time to build traffic. But you can also use an SEO plugin to help with search engines. And also set up an account and use Google Webmaster Tools – they have tons of good info.
This site has lots of good info: https://onecoolsitebloggingtips.com/
That’s site is on WordPress.COM, so some of it may be specific to that, but much is relevant to any site/blog.