Ex, I once worked at a company that required creation of a two sided market (buyers and sellers). I proposed that we bootstrap the market by creating a variant of our product to enter an existing, complementary market. By offering a cheaper solution in the complementary market with clear benefits for users, its likely we would have been able to establish a user base that we could then use to stimulate the seller side of the market, thereby achieving our goal of creating a brand new market.
The strategy our management consultant CEO went with was to put ads on LinkedIn.
Nobody works there any more.