Ask HN: Best way to have mouth publicity for startup without spending money?

I am co-founder of Rime (https://rime.co). Rime collects your publicly shared photos, videos, blogs, almost everything and puts in to one place that describes you completely. Whilst there are similar apps out there (e.g. HootSuite, Buffer), this is the first time a platform has been created, to bring all contents of users to one platform. Down the line we are looking ourself as Google for social search(content and people).

We have attracted more than 5K users in our platform and around 50 users active everyday. I want your advices to ramp up the user acquisition.