King air Captain on downwind for Runway 18R reports airborne conflict with another King air departing Runway 27. The Tower had called the traffic but did not accurately describe its' location.

Narrative

Approaching TPA we were lined up with our course line which was parallel to the active Runways (18L and 18R). We were about 1 mile west of 18R heading north in communication with the Tower. We had airline traffic holding in position on 18R in sight and acknowledged that with ATC. We also heard Tower clearing a King Air on Runway 27 so we were looking for that aircraft as well. Tower then told us that the King Air traffic was departing 27. We heard 'departing' so we were looking on the numbers end of 27 as well as where we would expect him to be rotating for climb out. Tower then asked if we had the King Air departing in sight to which we replied we were looking. The pilot flying at the time (First Officer) looked up to see the departing King Air right in front of us at our altitude. He pushed the nose over slightly but maintained our heading of north to avoid a collision; we then passed behind the aircraft. I do not believe the departing King Air saw us at all. It seemed that the Tower operator was in training as the 'supervisor' stepped in from time to time while we were on the Tower frequency. I wish that the Tower would have pointed out the departing traffic earlier in our approach. It would have been helpful to for the Tower to say the traffic was 'on climb out' verses 'departing.'