You can join Facebook groups (of companies you're interested in working with/for ). You can also do the same on Twitter (follow people from various companies and/or industries). But remember that following is just the first step. Make sure you like and comment on their posts. Add to the conversation so you stand out! Then, ask for an informational interview so you can learn more about them, their role at the company and their career track. Additionally, my friend recently told me about another website called meetup.com - so check it out!
I would go to meetup.com and join groups in areas of interest. I have used it to network with other professionals in my area.
More than just meeting people on social media (and you have some great suggestions here) I suggest that you find professional, trade or educational events related to the career you'd to have someday. These types of shows often have student passes that allow you to enter for free or at a very reduced rate. This is a great opportunity to meet people who share your interest.
For example, my daughter is studying to be an eye doctor. There are a lot of professional events all over the country for eye doctors and she has gone to many at no cost, and has met many people and learned many interesting things. Even product vendors are willing to show students their goods because they know that someday they will be the doctors buying the equipment.
I find that twitter can be useful in networking, especially if you follow and make posts within certain areas of interest. For example, if you are pursuing a career in marketing, you find and follow people and companies who have expertise in marketing and communications. This gives you the ability to stay abreast of the latest trends, but also helps you connect with people who are also interested in the same topics as you. Once you follow each other, then you can send private messages to each other to build relationships and network more effectively. Just remember that your social media account is a reflection of yourself and perspective and current employers may check out your social media presence, so be careful on what you post and who you follow or like.
Twitter and Facebook are two avenues to network.
Few more to consider :
there are so many sites to network, but I would start with what your interests are and your field of study or what you want to do professionally and look for sites around those activities - which will get you exposure to people that have your same interests and career aspirations. Be sure to look for the professional organizations that exist around your field of study and inquire on a Junior membership so you can attend meetings, seminars etc.
Don't forget networking opportunities in volunteer organizations - in many larger cities they have volunteer clubs that coordinate and match volunteer activities with people who want to volunteer.
Be active and get involved!!!!
I would suggest attending as many events (around school or college) and meetups (Meetups.com) as you can around you. Talking to people online is great, but meeting in-person goes a long way.
If you also want to work with someone, use https://rapportive.com/ or Email Hunter to find their email and reach out.
Good luck! :)