ACR X HAD CONFLICT WITH VFR ACFT IN CLASS C AIRSPACE.

Narrative

MSN TWR ASSIGNED X A 130 DEG HDG AFTER TKOF FROM RWY 18. OUT OF APPROX 1500-2000 FT WE WERE HANDED OFF TO MSN DEP CTL. DEP ASKED IF WE SAW THE ACFT Y AT 2 O'CLOCK. WE IMMEDIATELY SAW THE ACFT ON TCASII GO BY OUR 3 O'CLOCK POS AT OUR ALT LESS THAN 1 MI AWAY. WE ASKED DEP CTL IF THEY WERE WORKING THE ACFT AND WE WERE IN TURN. ASKED IF THE TWR HAD TOLD US ABOUT THE ACFT. WE TOLD DEP WE WERE NOT TOLD BY THE TWR AND DEP SAID TWR WAS SUPPOSED TO TELL US. OUR TCASII GAVE NO RA OR TA AND WAS SUBSEQUENTLY WRITTEN UP IN THE ACFT MAINT LOGBOOK. SUPPLEMENTAL INFO FROM ACN 307019: DEP CTL ASKED US IF WE HAD THE TFC IN SIGHT AT OUR 2-3 O'CLOCK POS. WE LOOKED AND DID NOT -- TCASII HAD A TARGET JUST OFF OUR R SIDE GOING FROM PLUS 0.1 TO 0.0. WE DID NOT GET A TCASII WARNING (WROTE UP FOR MAINT)AND DID NOT SEE TARGET. DEP SAID HE WAS NOW GOING THROUGH OUR 4-5 O'CLOCK POS AND TCASII SHOWED SAME AS WE NOW WERE ABOVE TARGET. TWR NEVER WARNED US ON OUR TKOF CLRNC. WE THINK ACFT WAS IN TFC PATTERN WITH TWR AS THEY WERE USING ALL RWYS AT MSN AND TARGET WAS AT AN ALT OF 1500-2000 FT. DEP WAS NOT WORKING TFC AT THAT TIME. DEP SEEMED CONCERNED AS WERE WE.