Our company has experimented with various social networks with varying levels of success. There are many out there, and which one is for you is hard to tell. Its really up to your potential fans to decide for you which social tools you use to build your business.

Forums
Our webmaster said, "Forums are out". And to some degree he is right. But, in and out are relative terms and there is a lot of information to consider when deciding whats in and out. Forums were more popular in the past, and their popularity is fading. On the other hand, they are still popular, and a wonderful way to exchange information.
+ Forums allow you to attract new clients who find your site and forum posts on search engines
+ New signups on your forum can become customers very quickly
+ Forum users develop a huge quantity of "User-generated-content" that shows up on search engines. 20% of our new clicks last month were from our forum due to the vast amount of information and keyword variations spread out on the 10,000+ posts it has
+ Forums allow you to discuss over a dozen topics simultaniously that will show up as "active topics", not to mention endless interactions on archived topics
+ Forums have a search function which allows you to query very select information. Forums are a great way to gather sorted information as well.

The advantages to the forum are tremendous and are not as easily obtained from other social networks. It is not a bad idea to have several social networks. My only advice is that you should not continue what doesn't seem to work well. Give every mode of social media a fair chance to build on itself before you judge it though.

Facebook
Our webmaster says that Facebook is the replacement for the mobile phone. We went from saying "Ooga booga", to having messengers on horses, to telegrams, telephones, mobile phones, but now there is Facebook which makes that all obsolite. 20 something-year-olds often don't pick up the phone any more, they go straight to Facebook to see what everybody is up to.
The main advantage of Facebook is that people like it. Customers send me emails daily asking me to be their friend on Facebook. Few are asking me to join other networks. Its easy to build a fan network on Facebook, because 40% of our customers are already on it and like it. Here are some advantages.
+ Facebook already has millions of fans, many of whom are already your customers
+ Your Facebook profile does NOT require a separate password. Once they login to their Facebook profile, they can visit ANY of their friends. Forums require you to login for each forum you go to which results in spam for the administrator, and password retrieval headaches.
+ Facebook is a fun way to interact. Post a topic and get lots of responses. Take polls, have contests, post links to blogs, enjoy!
+ Facebook can get you hundreds of quick fans using their pay-per-click advertising for your profile
+ Facebook can get you hundreds of new fans fast if you have some hot topics which get everyone enthusiastic.
+ Facebook has a welcome page which you can customize to promote a message that can be used to market products or networks.

Youtube
These days people are bored with text and pictures, they want video. However, creating videos is time consuming, particularly quality videos. If you can figure out how to make appealing videos and post them on youtube, that could be networked virally resulting in lots of new customers for you fast. The best advice is to put a few videos out there and see which ones are getting viewed and which ones are not. Then, invest more in creating more videos that seem to match the characteristics of the ones that were popular. Customer testimonials or how to videos stressing your company's branding are standard ideas for videos.

Twitter
This one is tricky. Twitter followers can grow fast under the right conditions. But, figuring out what they like is not easy. Our notary site does not do well on Twitter. The types of links we post do not get clicked on much, and we don't gain fans easily. The "Type" of people who like Twitter don't like us, and the majority of our current customers seem to intensely dislike Twitter as well. Its sort of like a new set of social class divisions. Its no longer what you drive, or how you look, or what you do -- its what social network you are on which defines you. What I did learn is that Twitterers like well written interesting, entertaining content. Don't give them TwitMonger or condensed language. Fully spelled out words and good content wins the prize. Go through your tweets that you are going to publish every week or month and think about each one. Should I tweet this or not? Should I rewrite this or not. Our retweet rate (the rate that followers forward tweets to their friends) TRIPLED when we took this care about quality. A professional company should seek the help of an expert Twitter writer. Keep in mind that regular writing and Twitter writing are a different animal. Someone who knows what Twitterers really want to read and retweet is worth their weight in gold.

Myspace
This is a very personal networking site and is not normally used for businesses.

Linked In
This is a professional networking site and is not recommended for promoting large websites.

The future
Facebook is the in thing these days, but in a few years, it could be something else that takes over. Who knows why someone new could take over the immense momentum that Facebook has. It could be simply because the hardware used in 2018 is so different from today, that someone elses site functions better on the new hardware. Or, it could be that another site has a completely different bunch of features and layout that people really like. Nobody knows, but it will be interesting to see how our lives are yet again revolutionized by technology.