To search for a person in Mexico, use a free service such as MexicoPhoneBooks.com, Facebook or the Mexican version of Yahoo, Mx.Yahoo.com. Additional options include traveling to Mexico, contacting known relatives, searching public records or using the Telemex phone company to do a search, although this option is only available for those who have an account with Telemex.
Consider whether there is a friend or relative of the person being searched for who lives in the United States. If so, contact that person and ask for the missing person's last known address and job. Also, contact other people in Mexico who have the same surname as the person being searched for. While this is time-consuming and can require contacting hundreds of people, it can provide good leads for those who have the time and patience to go this route.
Also, look through old emails and records on computers or phones, as there may be communication with the person. Additionally, look through old calendars and files for clues about where the person might be. If possible, find out as much about the person as possible, as this can provide valuable clues as to where the person is. Finally, consider hiring a private investigator if other methods don't provide results.