Hi there, based on your post, it seems that you just promote your app with social media, here i will introduce some other effective promotion methods for you,details as follows:
1. Take party in relevant activities
By joining relevant activities, you can expand your personal connections. Your app is about identifying books from quotes, then you can participate in some reading parties, sharing to your app to those members, and they are satisfied with your app, they will share your app to their firends.
2.Sponsor activities&contest
Most developers promote their apps online, therefore, app promotions are not limited to online promotion ways. Instead, some developers are marketing their apps by sponsoring activities &contest, like new book launch.
3.Post to forums
Find relevant forums to promote your app. Interested members will download your app and satisfied users will recommend your app to their friends.
4. Get ratings and reviews
4/5 stars ratings and positive reviews are the important references to users. To increase the installs of your app, you can incentivize users to leave good reviews and 4/5 star ratings. Of course, if you have enough budget, you can buy some ratings and reviews from third party, like reviewapp4u.
5.Use attractive screenshots
Take screenshots showing features of the app. They should be attractrtive to grab the attention of the user. This will increase the number of installs.
6.App store optimization
App store optimization is a process of optimizing your app to make it more visible and discoverable in app stores so that users are more likely to choose it from millions of other apps.A reporting data shows that 73% app installs is from searching app in app store. You can create a beautiy icon to attract audiences’ eyes, to attract them to click your app, then they may download it.