Some suggestions on how to pitch to journalists:
1. Pitch with a very interesting sentence headline (the title and headline needs to capture the journalist's attention and interest)
2. Convey an interesting storyline or something that is impactful. Everyone likes a good story.
3. Be concise and use associations that journalists can relate to. E.g. maybe your startup is the Uber for X or Airbnb for Y.

Some suggestions on how to search for jouralists:
1. Search for big publication's twitter account and find associated journalists' twitter handles. Send a tweet to the journalist. Concisely summarize your pitch in 140 characters.
2. Search for big publication's LinkedIn account and find associated journalists' Linkedin profiles. Send an Inmail. Refer to previous section on best practices in pitching.

You can get in touch through direct email or tweet with a catchy pitch.
To find personal email address you will have do little bit of research.
Also you should target only niche journalists who can understand and write about startup. To do this, search your product business category on Google News and get touch with journalists who recently wrote on that particular topic of yours.

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!