Historically speaking, here's as far back as I can find - the Least Used Station of every year, and the number of passengers that it had:
2009/2010 Coombe Junction, 42
2010/2011 Teesside Airport, 18
2011/2012 Teesside Airport, 14
2012/2013 Teesside Airport, 8
2013/2014 Teesside Airport, 8
29 days ago