toxic valentine has made some good points! The best way to garner activity on the site is to actively participate yourself, especially if you do blog giveaways or run a contest! Those options both require interaction from other users, and may even encourage others to do the same.
Hi! Site activity typically drops this time of year because people are tying loose ends with school and are committed to work, but activity will definitely pick up. Stories are updated a lot more regularly than people think and the site is monitored daily. Don't worry, there's still quite a few users left who use this site regularly, I don't see Mibba being too disused.
But, what I recommend anyone does to boost activity is join or create a contest, post more stories and poems (even short ones, so long as they follow the guidelines in the knowledge base), post more blogs with challenges and surveys and recommendations of users and their work, and make sure that you interact with fellow users.