"All the Colors of Darkness" (1963) by Lloyd Biggle, Jr, published by the SFBC in 1964.
The Universal Transmitting Company's breakthough stands to make its directors fortunes. Step into a booth in Manhatten and instantaneously you arrive at your destination, anywhere in the world. While hinting at the consequences for the freight, railroad and airline industries, "All the Colors of Darkness" mostly concentrates on a detective plot around this technological marvel. On the first day of operation, several "passengers" go missing, but these persons have no public records, no relatives and no one, but the teleport operators, notice their passing. Our hero is detailed to find them.