[@NuttsnBolts] is correct, I highly encourage you to look at other people's interest checks and first OOC posts to see what draws people in. good formatting and good aesthetics are a winning combination.

Another thing that really helped me out for my Danganronpa RP is that I scouted people before I even put up my interest check. I looked for people with Danganronpa characters in their avatars and struck up conversations with them over PM. Not only did I get to know some very friendly, loyal roleplayers, I was able to get feedback on my interest check before releasing it to the public. There's also strength in numbers. Sometimes all that's required to get people to join an RP is a few people showing interest. People don't want to wait weeks for an RP to start, so the more people who show interest day one, the better. Timing is also important. I unveiled my RP a week before Danganronpa V3 released in Japan, and westerners wanted a way to participate in the action. With things stacked so heavily in my favor, I got ten players in twenty-four hours. 

You might not be doing a fandom RP, but look at movie/game releases and see what everyone's excited for. You might have to tweak your interest check or idea so that it's more appealing to people. Even though this is your RP, it's something you're going to be writing with a few different people.