About 3 years ago, I was sitting at my desk at work, minding my own business, when I got an e-mail from a colleague inviting me to join LinkedIn. “What is this LinkedIn thing anyway,” I asked myself, “some sort of pyramid scam?” I thought highly of the person who sent me the invitation, so I went to the LinkedIn Web site to see what it was about. At the time, I didn’t see how it would help me, so I didn’t join.

A few months later, a summer intern who was working with me sent an e-mail inviting me to join his LinkedIn network. When I failed to respond after a few days, he confronted me. I admitted that I was not using the service. “I have spent years developing a professional reputation and building a network of colleagues and friends,” I told him. “Why would I want to show all that off to the rest of the world?”

More invitations came in. Eventually, one came from a very senior executive I regarded very highly. I could not refuse his invitation. I had no clue how a tool such as LinkedIn (or Facebook, or other social/business networking sites) would help me. I was now committed to finding out.

Your e-persona: It’s more than just LinkedIn

Even if you refuse to sign up for any social-networking sites, there is information about you on the Internet. Are you familiar with the term “vanity Google”? If not, search online for it, then search for your name. It’s interesting what comes up, isn’t it? This is your e-persona: the record of yourself as preserved and presented on the Web. Every employer considering hiring you will likely search online for your name. I do it with everyone who makes my shortlists.

Online social-networking sites can be a part of your e-persona, and unlike the Internet as a whole, you can control what is in your profile on these sites. For this reason alone, actively managing your e-persona through use of an online social network is a good idea. Like a well-composed résumé or cover letter, a well-constructed e-persona reflects a measure of thoughtfulness, professionalism, and competence. Whether it’s a personal Web site or your LinkedIn or Facebook profile, putting forward a consciously conceived professional image can’t hurt.

The corollary is also true: Sophomoric, sarcastic, or inappropriate material can be a lasting liability. Many stories circulate about employers who checked out a prospective employee’s Facebook page only to find embarrassing photos and comments.

Three good uses (and one really bad one) for online social-networking sites

Job searches: You can use online social-networking sites in a number of valuable ways for your job search. You can find contacts in companies or organizations that interest you through your network of friends and colleagues (and the people they know). You can research people in these companies and learn about their interests and backgrounds (a good way to prepare for interviews). You can also find people through your friends’ networks who may be suitable for an informational interview; informational interviews can be a powerful means of investigating careers and employers that interest you--and signaling your interest in them.

Professional networking: Even when you are not looking for a job, you can use online social-networking sites to scan for opportunities. Connecting with people in different organizations and understanding who knows whom within your network are very powerful assets for professional advancement. I've found it interesting to observe how my network connects to those of my friends and have discovered several independent mutual acquaintances. In a few cases, this unexpected link has led to new opportunities. Many social-networking sites have an array of functions and features that allow you to search for people: past friends and colleagues, people who do interesting work at interesting companies, and so on. Some of these sites allow you to post and respond to questions, get recommendations, or get introduced to other experts.

Social networking: Online tools can help you find new and old friends and get connected to fun things that have nothing to do with work. From the formal (Match.com) to the informal (Craigslist.org), to Facebook, there are numerous ways to find others with bizarre and obscure interests similar to yours. Staying connected to your classmates and alums from your past schools could be especially valuable; there's no clear distinction, after all, between your personal and professional networks. For foreign national grad students and postdocs, this may be particularly important: Your expatriate community can be a powerful and highly motivated resource network for you. Facebook allows users to very easily set up affinity groups of people with similar interests.

Collecting links and friends for the sake of high numbers (hint: a bad idea)

Even with a clear idea of what you hope to accomplish with these social-networking tools, it's easy to misuse or overuse them. I have come across profiles of folks on Facebook who claim to have more than 500 friends and folks on LinkedIn with 500-plus contacts; I suspect their definition of “friend” is more elastic than mine. If you linked to every single person who ever gave you a business card, you probably could, over time, accumulate 500-plus links. But how many of these people would remember you? And does this large but undifferentiated list of links do anything more for you than provide the world with a copy of your address book?

So, whom should you include on your list of links or of friends? If the person called you at work, would you take his or her call? If so, then he or she probably would be appropriate for your LinkedIn network. If this person called you on Friday evening, would you take his or her call? If so, accept their offer of Facebook friendship. Do you send out Christmas cards to 500 people every year?

It is okay to “delink” people from your network if you discover that the contact is not valuable or is never used; most sites make the “delinking” process invisible to the other party. Experts recommend that you periodically cull your list of contacts and throw out the ones who aren’t active.

The warm contact always wins

The power and sheer multitude of Web-based networking tools underscores a fundamental fact: Your real network, not a bunch of names in the "Friends" column of Facebook, is your most important professional and personal asset. Your network will be the source of your future employment, many of your future friends and colleagues, and, quite often, your spouse.

Online tools expand the ways you can connect to others, but they cannot substitute for face-to-face encounters. Whether in an informational interview, a professional mixer, or a social gathering, personal contact imparts momentum to your job search and professional life. If you have a choice between adding five more connections to your LinkedIn list or going out to lunch with a member of your network, choose lunch.

Comments, suggestions? Please send your feedback to our editor.

Image (top): Kelly Krause

Peter Fiske is a Ph.D. scientist and co-founder of RAPT Industries, a technology company in Fremont, California. He is the author of Put Your Science to Work and co-author, with Dr. Geoff Davis, of a blog (at phds.org) on science policy, economics, and educational initiatives that affect science employment. Fiske lives with his wife and two daughters in Oakland, California, and is a frequent lecturer on the subject of career development for scientists.

10.1126/science.caredit.a0800112