G.T.
We just trained our son, also at 2 1/2.
First, you can put his underwear under his diaper: this way the mess is contained (less washing for you) and he feels the wetness. The diapers are so efficient that children don't feel when they are wet. As a result, they can't associate the "need to go" feeling with the wetness result.
Then, make a big deal of the potty. We had a potty dance. It sounds ridiculous said like that but it works because at this age, they crave attention and are so happy to get attention! They want to go in the potty because they want the potty dance (or any other attention)
It worked for us. I still put him in pull-ups at night (the training ones with a drawing that disappears if wet). He has been 10 nights dry in a row. I just ordered a protection for the mattress and when I get it, he will go to sleep diaperless. He already wants to be without diapers at night and accepts them only to check the picture is still here in the morning.
Be patient, good luck!