In short, you should contact everyone you know (your 250) and everyone you do not know personally, but may be able to help with your job search. I realize that seems rather open-ended, so let's start with some specifics.
First, contact your relatives. Not just your immediate family—branch out into the family tree. And not just those who are "well-connected in business." Aunt Mabel may play bridge with someone who knows someone who is a Hiring Manager in your field. Remember, it's not necessarily who you know, but who they know.
Everyone knows someone.
Next, contact friends. Old and new, high school and college, neighbors and social acquaintances. They might even be a friend of a friend or relative, such as someone who plays tennis or golf with your parents. Spread the word. Some of the best contacts in this group are your college friends who graduated last year. They are already through the job search process and probably have lots of contacts (and free advice).
Next, contact every known entity within your college. Professors, advisors, administrators, counselors, coaches (they are often amazingly well connected!), and anyone else who has ties to your school. Beware that some in this group (especially some of the "academic purist" or "research first" professors) are not nearly as well connected with the real world as they would like you to think, but the guilt factor—their not wanting to admit this little secret—often pushes them to come up with some creative ideas. And be sure to reach beyond your circle of known alums to all alumni (recent or past) who are working for target companies, within your target geography, or within your chosen profession. Spend an afternoon at the campus Alumni Affairs office. This office is dedicated to networking with alums. They are usually more than willing to help, since you will soon be an alumnus as well. And you can't pay your dues without a job.
Also contact past and present employers, coworkers, professional associations, and social contacts through your church, synagogue, club, or other organizations. Make it your goal to reach out to your entire list of 250 and then some.