You have ways to keep track of non-posters....

No Posts:
SELECT userid, username FROM user WHERE posts=0

No Posts in the last 30 days:
SELECT userid, username FROM user WHERE lastpost=UNIX_TIMESTAMP(time()-(36400*30))

60:
SELECT userid, username FROM user WHERE lastpost=UNIX_TIMESTAMP(time()-(36400*60))

90:
SELECT userid, username FROM user WHERE lastpost=UNIX_TIMESTAMP(time()-(36400-30))

Year:
SELECT userid, username FROM user WHERE lastpost=UNIX_TIMESTAMP(time()-(36400*365))

Haven't visited in 30 days:
SELECT userid, username FROM user WHERE lastvisit=UNIX_TIMESTAMP(time()-(36400*30))

60:
SELECT userid, username FROM user WHERE lastvisit=UNIX_TIMESTAMP(time()-(36400*60))

90:
SELECT userid, username FROM user WHERE lastvisit=UNIX_TIMESTAMP(time()-(36400*90))

Year:
SELECT userid, username FROM user WHERE lastvisit=UNIX_TIMESTAMP(time()-(36400*365))

Of course you could always use the "Find" User feature to find these same users as well. You can use the "Email User" functionality to contact them also.