Unless you live as a hermit, your name will be available to others online. To find someone is "invisible", is highly suspicious to me. I think that simple fact tells me that I'm not dealing with a "modern person". If you search for me online, most of what you find, are things that I wrote, myself.
Join online groups: Choose the groups you join. Keep good company. The least visible groups are discussion lists. Usually they can only be seen by members. Your profile on Ryze or LinkedIn, and many other social networks is available to search engines IF you allow that option. I recommend that you do allow search robots to scan your page.
Become an active member: +80% of the people who join various groups do almost nothing after joining. With a minimal amount of regular activity you can be quite visible in most networks. Read what other people have to say. Visit the homepages of interesting people. Comment yourself on the issues under discussion. Participate, be a real member.
If real time chat is available use it: There is huge benefit in the simple process of spending time with someone else. Quite quickly you discover the personality you are dealing with. If you have good connection speed, Skype or some other VOiP programme will allow you to talk to people in far off places for minimal cost.
Connect to other people: By all means be a little selective in choosing friends or connecting directly to other people. But don't be too precious about it. On the contrary be generous. Many very experienced users tell the same story. When we started out, we sat idle when we should have been building connections, and we turned away far too many people we should have connected too.
Helping others: The best way to increase your own knowledge, confidence, and reputation, is to try and help others online. You very soon find out what you know and don't know, and it helps you to upgrade your skills. Forget the cost, if you can help; be helpful.
Online cooperation: There is huge potential for online co-operation but generally it's not happening, especially in a business sense. If you need people to help you, you need to be proactive in finding relevant people and inviting them to join you, in whatever activity you propose.