It was a bitch to manually get followers on Tumblr to sell t-shirts to. I had to seek users out, make sure they fit my target audience, and insert myself in the conversation. All without it looking like self‑promotion. That's a lot of mental energy just to reach out to one person. Once I built a fairly large sized audience boat loads of t-shirts started selling. Then I figured startups and businesses on Twitter would find it useful. And they did. Paying customers tell me it works 100 times better than Twitter ads.
If you're interested: http://audience.goodsense.io