Romero, 22, last played for Murcielagos FC de Guamuchil in Mexico's second division.
Chivas also added midfielder Peter Vagehas and defender Rauswhan McKenzie.
Vagenas, 33, of Pasadena, a 12-year MLS veteran, played 16 matches for the Vancouver Whitecaps last season after spending two years with the Seattle Sounders and nine with the Los Angeles Galaxy. He played his college soccer for UCLA.
McKenzie, 25, played in MLS with both Real Salt Lake and Kansas City.