An employee will be more attractive to employers when the employee is already employed but that does not mean that the employee should be looking for a new job while at work. This could easily get you fired. You are on your employers time and I know that if I caught an employee searching for another job while at work, that would give me the impression that the employee does not want to stay so I would grant them their wish and let them go. So if you want to look for another job, just do it on your own time at home.
http://www.thirdage.com/your-career/looking-for-a-job-while-on-the-jobHave you ever searched for another job while at work?