Since you said you aren't currently charging anything for it, I would say you should wait to see if the market will validate it before shutting down. I.e, see if you can raise the price to something > $0 before calling it quits.
With the small number of active users, perhaps you should look at selling your technology to a company that will be able to spend on marketing.
facebook had a serious trouble monetizing it's service. so no revenue or monetization method is not enough for deciding that this business is not worth it.
This will have a negative impact of high churn rate for sure. But if I will shut it down, then churn rate would mean nothing - it will be shut down anyway!