I was flying a Piper Navajo thatvseats 8 passengers out of a small airport, we were making all of our required radio calls, but because this was a small uncontrolled airport some people in small airplanes will operate without radios or just dont care enough to broadcast their position. Anyway we were doing our due diligance but not long after take off and while leaving the traffic pattern my FO says "shit!" And takes control from me and make a relativley aggressive (for passengers at least) turn to the right. As he does this i see a cessna out my left window no more that 150 ft below us. We essentially climbed through the altitude he was crusing at and turned to avoid him. Only one passenger noticed when we got to the destination and he told us it was a "good move".