When I first started, I didn't really understand how Webtoons worked. I put my comic in the wrong category but updated once a week, so readers knew the schedule. In the first 5 months, I gained 600 subs. After I switched to a more relevant category, Romance, I gained 1000 subs a month until Oct '17. This is with no promotion from Webtoon, no-cross promotions, or promoting on other social media.
If you really believe in your project, don't give up! I've seen comics start off really slow, end up getting promoted by Webtoons, and quickly reach 25k+ subs. Also I've seen comics that have been around for over a year that never reached more than 1K get promoted and now are at 60k+ subs.
Good luck! 