No one job search method will reveal all of the jobs out there. Not every kind of job or industry is represented in every job search method. For example there are many jobs you will not find through the On-Campus Interviewing Program, and there are many jobs you will not find posted on Internet sites. If you want to maximize your options, you will need to use multiple methods. That means at the beginning of your final year if you're graduating, and it means in fall if you're looking for a summer internship.
Some employers look for hires and recruit many months in advance of the anticipated work-start date.
If you don't start early, you can still find opportunity, but you will have missed out on some of the options. Learn how others pursuing your career field or industry have been successful. Don't limit yourself to one source. Talk to faculty in your department. Talk to alumni volunteers you find in VT CareerLink .