Matching by Name--either manually or via systems built into FileMaker will be problematic as different people can have the same name. You might want to assign ID numbers if at all possible.
Sounds like you need two tables. One table where you have one record for each person and another where you have one record for each "sighting" and then you link them in a relationship.
People::PeopleID = Sightings::PeopleID
Then you can define this calculation field in People to get your list of locations separated by commas:
Subsitute ( List (Sightings::Location ) ; ¶ ; ", " )
Then a list view layout based on People can be used to produce the report you describe.
If you insist on matching by names, you can use name fields in place of the ID fields, but note that you were warned about the potential complications involved.