Agreed! You should try a fan page on Facebook and Start a Group on LinkedIn. But I answer might change depending on what you are trying to promote or sell. Let's not forget twitter-tweet three times at least, follow people likely to buy your product or service.
You need to stay away from getting traffic at sites that have no competition. This is the biggest mistake you can possibly make with your business. You need to make sure that you go where other people are going as they know what they are doing. Follow the crowd when it comes to traffic generation and go where other good marketers are going so you can get the good traffic they are getting that is turning into buyers for them. It might be a bit harder, but you need to realize that if there is a lot of people trying to get the traffic, then it must be working.