Samothracia was an island, about 8 miles long and 6 miles wide, in the northern Aegean Sea off the west coast of Asia Minor (i.e. Turkey). Samothracia takes its name from a region of the mainland known as Thracia i.e. Samothracia means Thracian Samos. It is mentioned in Bible History during Paul's Second Missionary Journey (see also Paul's First Missionary Journey and Paul's Third Missionary Journey) when he sailed from Troas in Turkey to Neapolis in Macedonia.
"Therefore loosing from Troas, we came with a straight course to Samothracia, and the next day to Neapolis"
Paul's first missionary journey was focused in Turkey; his second missionary journey began there as well, where he was accompanied by Silas and Timothy / Timotheus.
"16:1 Then came he to Derbe and Lystra: and, behold, a certain disciple was there, named Timotheos, the son of a certain woman, which was a Jewess, and believed; but his father was a Greek: 16:2 Which was well reported of by the brethren that were at Lystra and Iconium. 16:3 Him would Paul have to go forth with him; and took and circumcised him because of the Jews which were in those quarters: for they knew all that his father was a Greek. 16:4 And as they went through the cities, they delivered them the decrees for to keep, that were ordained of the Apostle and elders which were at Jerusalem. 16:5 And so were the churches established in the faith, and increased in number daily." (Acts 16:1-5 KJV)
It seems that Paul had intended to remain in Asia Minor for his entire journey, but Christ decided that it was time for Paul to extend his ministry (see Paul's Ministry) into Europe. Hence, the vision of the man from Macedonia.
Sailors in ancient times did not have the use of modern-day weather forecasting or navigational technology. Ship's masters preferred to keep land in sight whenever possible (see Coasting), so it was a natural route to sail past the island of Samothracia in their crossing of the Aegean from Troas to Neapolis.
Most of the first Christians were Jews; Christ Himself was a Jew (see The King of the Jews), as was the apostle Paul (see also Was Paul A Jew or a Benjamite?). Paul found fellow people of God in Macedonia who were ready to recognize that the long-awaited Messiah had come.