Millions of businesses join digital platforms each year, yet little is known about their success rates or how platforms manage their entry. Using data from a leading Chinese e- commerce platform, we show that fewer than 1% of new, ID-verified sellers become successful small-to-medium-sized businesses. Analysis of consumer search sessions reveals that consumers prefer entrant products over incumbent ones. Further, increasing entrant exposure on the margin increases overall purchase rate of a search session, indicating that entrants are under-explored compared to social optimum. Finally, we revisit an earlier intervention that increased entrant advertising by 2.3%. We find that it slightly alleviated the under-exploration of entrants, albeit statistically insignificant.