He was popular enough among the Jews for Herod to see him as a threat, but how many people outside of Palestine actually heard of him?
His baptism was well known way beyond Palestine if we can believe anything we read of in Acts. 24Now a Jew named Apollos, a native of Alexandria, came to Ephesus. He was an eloquent man, well versed in the scriptures. 25He had been instructed in the way of the Lord; and being fervent in the Spirit, he spoke and taught accurately the things concerning Jesus, though he knew only the baptism of John.
Paul himself had to write to the Corinthians because Apollos was infringing on his turf.
"I have been told . . . that there is quarrelling among you . . . that each of you is saying: 'I am for Paul,' or 'I am for Apollos,' or 'I follow Cephas' or 'I Christ'." (1 Cor. 1:11-12)
Josephus apparently wrote of him while in Rome.