I have over 1000 followers on Dribbble, and people there are typically supportive of others launching things, so that helped too.
On Forrst, I used the promoted post option ($40 for 2000 impressions), but it didn't seem to matter much, because it started generating referrals after the promotion expired. And generally speaking what you want on Forrst is for your post to be upvoted by Kyle (the founder), because everyone is following him by default and his upvote makes your post show up in pretty much everyone's feed.