Thais address one another by first names and titles and reserve last names for very formal occasions and written communications. Last names have been used in Thailand for only the past fifty years and are difficult even for Thais to pronounce. Two people with the same last name are almost certainly related.
Foreigners are often addressed by their given names because it is easier for Thais; it does not imply familiarity. Thais will probably call you Mr. Joe or Mrs. Mary.
Titles, rank and honor are very important. Introductions require only the given name and title. Mr., Mrs., or Miss + family name are appropriate for visitors to use in formal situations.