Looking for suggestions on modeling organic user growth.

Investment team is asking for projections - "where will be be at the end of 2020?". I give them the answer of, depends on paid media and organic growth/WOM. We all know you can't rely on "viral" spread, soooo... any suggestions on building out this projection model beyond paid media. Is it worth the exercise? BTW - our Beta v1 is launching in 2 weeks, so we have ZERO data.