The migrants -- three men and three women -- left Juan Dolio Beach in the Dominican Republic on Dec. 17, the Miami Herald reported.
The U.S. Coast Guard became involved when the migrants' boat failed to arrive in Puerto Rico and family members in the United States alerted the Coast Guard.
Rescue crews searched about 22,000 square nautical miles around the Dominican Republic and Puerto Rico, including an area called the Mona Passage.
"While the fate of the people may never be known or what happened to them, our thoughts and prayers are with their families and loved ones during this difficult time," U.S. Coast Guard San Juan Cmdr. Drew Pearson said in a news release Wednesday. "For those who know of a loved one attempting to make the illegal voyage across the Mona Passage, do your best to reason with them. Tell them to not go out to sea, to not entrust their lives to a smuggler, and to not attempt the treacherous voyage. In doing so, they risk losing their lives."
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