Firstly, a disclaimer – don’t spam Reddit and other similar sites hoping to “hit the jackpot” of referral traffic, because it’s not going to happen. Members of communities like Reddit are extraordinarily savvy to spam disguised as legitimate links, but every now and again, it doesn’t hurt to submit links that these audiences will find genuinely useful. Choose a relevant subreddit, submit your content, then watch the traffic pour in.
Do you have an older list that you suspect has mostly decayed? Create an engaging opt-in message and send it to your old list encouraging contacts who wish to re-opt-in -- promising to remove all contacts who don't respond. Though it might seem counterintuitive to remove folks from your email lists in order to grow them, emailing only engaged contacts could improve your deliverability and increase the odds of your email getting shared with those outside your current contacts database.