Main thing is to look at the time of the contact report, if it was more than 12 hours ago you might as well forget it.
If it's a new one, some simple math and geometry works. Figure 10 knots as an average, in 5 hours it will have moved 50 miles, in 24 hours 240 miles. Draw the course line, then measure off several points for where he should be (unless he changes course) 4 hours from now, 8 hours from now, 12 hours from now, etc. Then measure off an intercept course that will put you 10 to 20 miles ahead of him when you reach the course line, the angle will depend on your speed.
After that you turn to the reciprocal course (opposite his heading) and if you don't have SJ radar set up a zigzag 10 miles either side of the reciprocal course.