If you know the journalist's name, your should reach out to him/her directly. If you don't yet have a name, then read the publications your interested in and check out the authors of the pieces that you find applicable/interesting for your business. While you can try email/twitter/LinkedIn, I have found that the best way is still to just call the person in question and have a short conversation with them. It's the most personal way and you can immediately answer any questions that the person might have. It might also be that the person refers you to another colleague more suitable for your request or that they give you advice on what the best approach would be for your kind of request. Trust me, nothing beats personal contact!