When I last worked in a consumer tech startup, our best ROI by far was paying tech youtubers or doing targeted ads to tech categories on youtube. Being in a startup I was vaguely aware of marketing efforts but I was never involved directly, so I can't say why or how that was discovered. All I know is my coworkers dealing with marketing said the roi and conversion rates specifically for youtube far outstripped traditional targeted tech ads through google or facebook. Of course this may have been because we weren't great at advertising, so your mileage may vary.