The important question, of course, is why you should go to the effort of building an open source community around your code. The answer is self-interest. Aside from occasional PR moves, no one opens their code out of purely altruistic motives. You open your code because you stand to benefit from doing so.
You only benefit from opening your code if other people contribute to it, which requires that you build some form of community around the code. A community doesn't have to be a group of individual contributors; it can be made up of companies that have a vested interest in funding parts of development. It also may contain a large number of transient members who drift in and out.
The exact structure of the community depends a lot on the nature of the code and its potential uses. In some cases, building a community is very difficult, but you may find opportunities in seemingly unlikely places.