Yes they did. Before 1808, American ships flying the American flag, crewed by Americans sailed to West Africa, bought slaves there and imported them into the country. The Americans participated in the slave trade. We were not the heavy weight hitters of that trade, only about 2 or 3 percent of slaves were carried on American ships but we did participate. After the importation of slaves became illegal, Americans continued to be involved in the slave trade. Instead of coming to America, the slaves went primarily to Cuba and the other Caribbean islands. Often American slave ships would sail under false flags. In addition to direct participation in the slave trade, American ship yards built ships for the slave trade, American banks lent money to pay for the voyages, and American insurance companies insured the ships and the black ivory they transported.
It was European ships, initially Portuguese/Spanish ships that transported the vast majority of slaves to their plantations in the Indies and South America. Later the British became the main transporters. It was Europeans that had the licenses to purchase slaves.
This isn’t to say Americans were more moral than the others. Rather, America didn’t have the ships and early on didn’t even have a Navy to protect them on the high seas. Some Africans did come in on ships flying the American flag. Some came from the Islands of the Caribbean up as north as Boston. Yes, Boston had slave auctions. Other American ships were those engaged in smuggling slaves. But we’re talking a minuscule number relative to the Portuguese, British and other European countries.
For fun, try telling someone from Boston or from Portugal, Spain, England or any of the European countries about *their* involvement in the slave trade. They’ll say, Oh no, it’s the US that did all the trading and the shipping. The US owes reparations, not us.”