How to increase demand for a product?

Solution 1:

There is no demand mechanic as everybody has said, there's simply a truck spawn timer that spawns regional trucks to either export or import goods. The more regional truck bays you put on your trade depot the more trucks will come in to export/import goods.

Anyways, that's not your problem.

If you have everything set up right and no traffic, here's more than likely your problem: There is currently (as of 03/26/2013) a regional trade truck bug which causes trucks to get stuck on the regional highway near the entrance of another city. This causes huge problems and results in excess storing up of your goods. I've seen this reported to Maxis programmers several times and a patch is incoming to fix it.

Solution 2:

Be sure you click the “Manage Global Deliveries" (select the Trade Depot) button and select "export" for the resource you want to sell. (You need to do this separately for each Trade Depot/Port.)

The global market provides the trucks. See https://gaming.stackexchange.com/a/110069/30220

(There is no "demand" mechanic for resources.)

Solution 3:

The demand shouldn't be a problem, just make sure you have no traffic problems between the trade sites and the regional highway