The album's second single, "Girlfriend", written by Charlie Mason, was released early October 2013 and debuted within the top fifteen in Spain. The third single, "Lánzalo", written by Jacobo Calderón and Mateo himself, was released in March 2014 as a charity single, in support of UNICEF campaign for the children who suffer as a result of the Syrian conflict. The song debuted at number two on the Spain's Top 50 singles chart.
The AM tour started in February 2014 in Valencia and, after almost 40 concerts around Spain, ended in September 2014 in Málaga. In October 2014, Mateo headlined the "Coca-Cola Music Experience" concert at a sold-out 15,000-seat Sports Palace, in Madrid.
In November 2014, he gave his first concerts in Latin America: at Sala Omnium, in Santiago, Chile and at a sold-out 7,000-seat Luna Park arena, in Buenos Aires, Argentina.
In May 2014, he traveled to Los Angeles to work on his third studio album with Damon Sharpe, Lauren Christy, Andre Merritt and other songwriters. The album, titled Who I AM and released in Spain and Latin America in November 2014, is a collection of broken beats, throwback funk vibes, futuristic beats and organic arrangements. A special edition of the album followed in June 2015, featuring guest appearances by Dvicio, Critika & Saik and Lerica. Who I AM peaked at number one in Mexico and Spain and was certified Platinum by Promusicae.
In September 2014, he released the first single "All The Girls (La La La)", a song written by Lauren Christy, Jacobo Calderón and Mateo himself, which peaked at number 9 on the Spain's singles chart and topped the radio charts in Brazil. The music video for this song was chosen as the best Spanish music video of 2014 on the VEVO platform. The album also included the singles "Todo Terminó" and "Another Heartbreak" featuring Dvicio's vocalist Andrés Ceballos.
To promote Who I AM, he embarked on a tour to Colombia, Chile, Brazil, Argentina, Dominican Republic and Mexico. In this last country, Mateo performed with Carlos Rivera at Teatro Metropólitan and with the Mexican boyband CD9 at Mexico City Arena. The Who I AM concert tour began in December 2014 in Barcelona and ended after nine months and almost 40 shows, including a big concert at Sports Palace, in Madrid. He held his first solo concerts in Mexico City, at Plaza Condesa, and Peru, and his second sold-out concert at legendary Luna Park arena, in Buenos Aires.
In November 2014, Mateo's first biography, I.AM. was published by Montena, an editorial part of Penguin Random House.