The distribution channel of an OA journal, is the internet. Other distribution channels exist for non-core deliverables like paper editions, but the major product is scientific content, which has an electronic distribution on the internet.
Being on the internet does not, however, ensure that you can deliver what your customer needs. Your primary customer is the author, and authors want readers. How do you ensure a large and relevant readership to your authors?
There are many factors to this, some are technological others are more a question of policies and work.
Make sure your journal is indexable, and indexed by relevant services. Google indexes almost anything, but database parameters or login requirements may prevent Google from indexing you. Make sure this doesn't happen, today web sources that can't be found on Google won't be used.
Google Scholar only indexes specific sources that they have checked for quality. If you publish your journal by putting pdfs on your institutional web pages, chances are good that Google Scholar will not index you. You should try to organize your journal in a way that makes it possible for Google Scholar to index you, and contact them to get them to index you.
The more links there are to your journals or articles from other websites, the higher you will rank on Google and the more likely you are to be found among the first search results on Google.
is a protocol that allows services to harvest your metadata, and make your content available through them. Using a publishing solution that is OAI-PMH-compliant makes it more likely that one or more such services will harvest you, this increases your visibility on the net and your Google ranking.
DOAJ, the Directory of Open Access Journals, is a service run by the University of Lund. Many library catalogues and services harvests data from and through DOAJ. As a first step, registering your journal in DOAJ will increase readership.
DOAJ also offers the possibility of uploading article information to them. This information is also harvested by many library systems, so uploading to DOAJ actually will make your journal available in institutional journal indexes/databases at universities all over the world, thus increasing readership.