Are there any research paper/studies available on benefits of online/mobile advertising for small businesses? Can't find anything useful on duckduckgo. Before

Are there any research paper/studies available on benefits of online/mobile advertising for small businesses? Can't find anything useful on duckduckgo. Before fb/google small business seems to serve local demographies (mostly?), not sure how much they really benefitted by going/selling online. Eyeball-to-real-cash. Or may be they are just brain washed into online advertising benefits when there aren't any.