Four Rockville massage parlor operators have been charged with using their businesses as fronts to conduct prostitution or human trafficking, according to Montgomery County Police.

The investigation was launched in September after authorities noticed an increase in advertisements for acupressure businesses and massage parlors on websites, Montgomery County Police said. Police said they conducted searches of six Rockville businesses and filed charges against operators of four of those establishments.

Mauricio Alex Garcia Guardia, operator of Executive Body Work, was charged in a warrant with human trafficking and conducting prostitution, police said. Feng Liu, operator of YaYa Spa, and Howard Hao Wang, operator of Tropical Spa, each are charged with human trafficking and conducting prostitution. And Pink Spa owner Roberto Carrasco has been charged with conducting prostitution.

Authorities are asking anyone with information about the suspects or businesses to call 240-773-5958.