Today, LinkedIn is the most dominant and efficient professional social network. LinkedIn also features job openings (see the “jobs” link underneath the search bar at the top of every page). In addition, visit the Jobs tab in LinkedIn Groups (you can join up to 100), and the company profile pages for your target employers.
LinkedIn is one of the best online venues for engaging with individuals who are employed at your preferred companies (and people who are former employees). Use it to make a connection with the employer, too. You can also uncover job postings and employer/company pages which offer you details about the company along with how you might be associated to existing employees.
Utilize LinkedIn to interact with people who attended the same schools as you, even if you didn’t attend the schools at the same time. Alumni networks can be very effective. Locate people who attended the same school as you and find out which of them are employed at your preferred companies — that’s a starting point for broadening your network.