First up you'll need a micrositetoshowcase your app. You should have a press page.

I really wish I could link you to Christopher Phins talk at NSConference 5 on how to handle the press, but it's behind a pay-wall. It was a good explanation from the other side about how to present your app.

WRT it being a reddit app, you should probably go to the source of your users too. Maybe /r/ios7 or look where people are talking about reddit apps.

Ensure it has a twitter account so people can comment publicly, respond in kind and thank people for constructive criticism. Use it to try and gauge ideas and get people interested.

Finally, you should check out how your competitors are building their community, e.g. I know of biscuit@biscuitapp because the developer is a nice guy in the dev world and I've seen his announcements on reddit somewhere.

There are two main ways that SaaS products are marketed that apply to other areas as well:

• App goes viral • Pay for traffic

Orta is right about going to the source - go to where your target users are and have discussions with them.

The app should have a Twitter account; there are services you can use that will auto-follow people on Twitter that fall into a certain description and then auto un-follow after a certain amount of time if they don't follow back. It's a little underhanded but can be effective and I know that this one in particular is very good about not breaking Twitter's TOS for this: http://tribeboost.com

You can use this site to set up daily email alerts for Twitter. Your alerts can target prospective users or keywords to help you find people that might be interested in your app: http://warble.co

Really though the best way to market your app is to do something viral that will get passed around the Internet thousands of times.

Try to get mentioned in relevant newsletters (Netted by the Webby's) is a good example of this.