General:
* Everybody: Suitable when you mean *all people*, without exception.
* Every single person: Emphasizes that absolutely everyone is included.
* All: More formal than "everybody."
Specific contexts:
* Somebody: When you're looking for a single person, even if you don't know who.
* Someone: Similar to "somebody," but perhaps slightly more formal.
* A soul: More poetic and archaic, implying any person at all.
* A single person: More formal and emphatic.
For emphasis:
* Anyone at all: Highlights the lack of specificity.
* One person: Emphasizes the singular nature of the subject.
Ultimately, the best synonym depends on the specific meaning and tone you want to convey.