you can't just swap pins around and hope
(well you can but the magic smoke will soon leak out if you do)
a) you MUST have a resistor between base and arduino - to keep the magic smoke in the arduino
b) you have emiiter and collector the wrong way round - transistor will work backwards, but very badly and the smoke will soon leak out
c) you MUST put a reverse diode across the motor, the back emf will kill the transistor - and you know what happens to the magic smoke!
d) did you try connecting the resistor to +12? - it will turn the transistor off - and the motor should stop
I can't tell which transistor you are using so can't tell if E B and C are correct
also what size motor is it? (no not inches - current rating!)