The major challenge in using networking as a job search tool is that networks are hard to build and maintain. In order to create a worthwhile network, you need to aggressively go out and meet people who could be of use to you in your career. You then have to maintain contact with these people in such a way that they will remember you and be inclined to think of you or help you in a job hunt situation. All of this takes time and a great deal of effort. This is the greatest challenge in using networking as a job search tool.