Moving forward with a passive candidate is much different that with an active candidate. An active candidate is already sold on looking for a new job and is thus very open to hearing what open jobs are out there. On the other hand a passive candidate, is just that passively looking or maybe not even looking for a job. Thus, a recruiter must take a unique approach to passive candidates.
To a passive candidate, it is best to sell the discussion, not the job. With passive candidates, I ask them if they are open to either a networking discussion or a career development discussion.