How to get writers to take the next leap on my website?

I run a sports blogging website for beginners. When I reach out to people, I get a lot of interest. Half of those people end up registering on the website. I do wish more would sign up but that's a problem for another day. Anyway, Very few take the initiative to start posting after signing up. This is where I am making a mistake. I need to know how to approach it from there. How do I get them to start posting and become reliable? I am unable to pay them at the moment and they are aware of that before signing up. Is making a schedule or deadlines appropriate? I don't want to seem pushy, as they are doing me a favor. Since there are many teams, I tend to forget/confuse the writers. What is a good way for documenting this information and staying organized? Thanks!