There is no magic trick to buzz. It mostly involves a lot of emails and connecting with journalists, bloggers, people on twitter, etc. Getting buzz can also be called influencer marketing. You find who the influencers are, then get them excited about your product, etc. When one of my projects was featured on Hacker News and got 10k visitors it was because of a single tweet that an influential person did.
The rest is just having a PR strategy.
Just like you have honed in on your market fit, you also need to hone in on marketing and PR fit. This means you should create a target list of on-brand publications and bloggers where your product would resonate with their readers and your potential customers. Ideally you would also follow individual journalists that have written articles on similar or complimentary companies and services. No two publications are alike and usually you will want to go after influencer sites that can get your company out there to important people. Influence is much more important than page views and size, and in many cases these key sites will be picked up by dozens of other sites. Really explore this area because these influencer sites might not be read by your potential customers, but they might be read by many grass roots bloggers and other publications. Targeting really is key.
After you have a nice target list of publications, journalists, and their contact details, your next step is to craft a story and narrative. The best pitches usually have the best stories that are less about details and more about vision/innovation/disruption/adversity. This is different for everyone, but for you it could be how your company is creating new jobs, or creating new industries, or disrupting old ones. How have peoples lives been changed? How are you making that happen? You should keep the story rooted in truth but a little hyperbole can go a long way too.
Next up is your pitch. Take the essence of your story and cater it to each journalist based on their previous stories, personal interests, etc. For important publications you might want to add an incentive they can't refuse, like something free for a month, and a giveaway where 5 of their readers can receive a free assistant too. For other pitches I have sent freebies and iPod touches to various degrees of success.
Then start at the top of your list and work your way through. This can be incredibly time consuming and the amount of success you have will largely depend on how tailored the pitch is, how good the story is, and what your angle is. I wouldn't bother with press releases. One caveat: be careful with pitches because a journalist often doesn't want to cover something that their competitor just did. In this case timing and priorities are crucial.
Create a PR calendar that features important dates and tech milestones that show your product maturing.
Going beyond standard PR, I have seen collaborations go a long way with small to medium sites. For example, partner with 10 publications/bloggers and have a giveaway. The users who use the most hours/do the most tasks/use the assistants for a scavenger hunt/use your imagination get a free MacBook Pro. A giveaway for giveaways sake doesn't get a good return, but a giveaway that integrates with your product and gets people using the service goes a long way.
Lastly, make sure you have analytics setup so you can evaluate what worked and what didn't. You want to learn a lot for your future PR activities.
Unfortunately, the author has asked to remain anonymous.