http://steamcharts.com/app/99900
Came across this handy tool. It seems that the games playerbase peaked during August 2013. Overall the game seems to have been able to get above 1k players pretty consistently besides these past few months.
Also, please note that this data is only from people who play from Steam. Standalone client users are not included.
Oh hey, you stumbled across the one piece of source data that people who have been whining "this game is dying" have been pointing at for the last four years like a child nagging their mum in a toy store.