Amphipolis was situated about 30 miles west of Philippi on the Via Egnatia. Luke remained at Philippi while Paul, Silas and Timothy continued to Thessalonica. There is no indication of any preaching done in Amphipolis and Appollonia. In fact, the reference to the city barely attracts notice.
Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where there was a synagogue of the Jews. (Act 17:1 ESV)
The River Strymon runs past Amphipolis and continues for about 3 1/2 miles south where it flows into the Aegean Sea. The photo of the River Strymon below was made in the late afternoon against the sun, but I like the effect.
K. L. McKay, in an article in The New Bible Dictionary, describes the city briefly:
Prized by the Athenians and Macedonians as the key both to the gold, silver and timber of Mt Pangaeus and also to the control of the Dardanelles, it became under the Romans a free town and the capital of the first district of Macedonia. Amphipolis is about 50 km WSW of Philippi on the Via Egnatia, a great Roman highway, and Paul passed through it on his way to Thessalonica (Acts 17:1).
The city is somewhat difficult to reach and there is little is to be seen.