With 17+ years in PR, and my work as chair/co-chair with the MIT Enterprise Forum in Chicago, let me add to what has already been said.

You have two industries (aka targets) to approach - technology & advertising. Try to include a demo video in your media pitch/kit.

Create and tell a story to reporters as to why you created your startup. What need did you see? Is it from personal experience in the ad industry? Something you experienced that was a real pain. Something that you said to self "there has got to be a better way."

Find out from your financiers who they have funded and then research to find out which reporters wrote about those companies. I would also suggest putting out a press release. PR Web is relatively cheap, and can help with SEO. If you need a media list I also have a suggestion. Feel free to contact me.

What sets you apart? Build a compelling kit around this information and/or hire a pro to do the same. Then it's pitch time / relationship time. Reach out to me for more.

First, you'll want to build a media list to contact. Careful research will help you develop a targeted list of reporters who would be most interested in hearing about your company. Once you have your media list in hand, the key is creating the right pitch to contact them with and knowing how to approach them properly. Drop me a line if you would like any guidance since this is what I do all day long.

Get a bunch of your craziest wackiest friends over one night.. Get into your favorite bottle of spirits.. Bring out a white-board and ask a single questions to be answered by the end of the night:

What can we do with our product/service that will be so entertaining and memorable that at the very sight of it, people can't help but to talk about it... (Think - Jean Claude Van Dam - Volvo stunt) Or (West jets christmas giving video) there are endless examples of demonstrations of product services that the media would love.. Believe it or not, when you are having the most fun, are the most carefree is when you are most creative... (Hence the spirits- teeheee) Anyhow, when you finish the brainstorm.. which should be probably after a bottle or two.. you'll have everything you need to have a story.. You just have to trust you gut and pick the most amazing, fun, enjoyable, example of your best product/service demo, and you better believe if you can't wait to show people... They can't wait to show it to others.. that's how you become.. Newsworthy....
Just my two-cents...
Steph

You have received good advice but I would also ask what is the goal of your PR efforts? Is it to drive awareness, gain leads, etc? Before beginning your outreach it's important to understand what you want to accomplish. This in turn will help you to craft outreach that matches your goals. You get journalists to write about you by telling them succinctly why they should care. Why would they and by extension their readers care about your story? Go beyond gathering target publications and names to understanding those you are targeting. Get to know them and not only their beat but their preferences. In addition, don't limit your outreach to trying to get journalists to write about you, offer content. Bylined articles are a wonderful way to establish thought leadership.