Basically:
1. ‘Someone’ is used if we don’t know the
person and there are many people to decide from. The use of ‘somebody’
is when we refer to a person but in a narrow amount of selection.
2. ‘Someone’ sounds personal, exclusive, and formal. ‘Somebody’ sounds vague, informal, and distant.
3. ‘Someone’ is more appropriate for formal writing whereas ‘somebody’ is slang, casual, and unofficial.
4. ‘Someone’ is pleasing and likable; ‘somebody’ lacks engagement and appeals only in limited occasions.
5. Both words have indistinct proper usage; both have minor differences. (se refiere a que las diferencias son mínimas).
