Because of the prospect of the Tees Metro, Im pretty sure there will be some increases because of people being able to actually get to the airport, due to the loss of the bus links by Arriva, there is a need!
As paarmo has said, there have been huge increases in use of Teesside manufacturing industries, and Hartlepool is also one to show for that. What we need is trains to stop there for the time being, to keep that small amount of passengers going. A train every hour would do it, meaning the through Saltburn - Darlington trains would stop every 2 trains - atleast its a frequent service, and the airport can boast good transport links to major north east areas. From Thornaby, there's links to Hartlepool (to London by Grand Central), Newcastle, Hexham, Manchester Airport, Leeds, York and many more. This atleast gives the airport some kind of service in which it requires - the bus was not quick enough as it had called at (From Middlesbrough) - Stockton & Yarm. Therefore taking the long route round.
The airport also needs new management, and management that care about the airport, not just whats in their wallets. Im sure a majority of you will agree - DTVA staff are lacking, quite badly, in the management fields.