A quick easy (but a bit dirty) trick is to post in a couple appropriate sub-reddits asking for a solution to a problem your app solves and let the comments organically populate. Make sure your question will be worded similarly to a search query on google. Come back a few days later after nobody is looking at your post any longer and edit your question to say you found a solution and link to your website. This is sometimes an effective way to get traffic via search since so many people append reddit to their search queries.

Also, you could just reply to your question with a link to your app under a different account but I'm not sure this as effective as having the link in the post which guarantees the link will be seen if someone clicks on that Reddit thread via Google, otherwise, there is no guarantee that your comment will get up voted and be visible, unless of course you game this also.