Review Insert/Update stored procedure
I'd rather use the FacebookAuthorId and FacebookLocationPostId as primary keys, because your logic ensures them to be unique. In case of your current solution you would still require (unique) indexes on these fields (in order for lookups to be efficient) so there is no reason not to use them as primary keys.
Given suggest optimization you don't need to check/insert an author record   LocationPost_Save, just use the merge to insert/update the data in the table, and create a separate Author_Save SP that will do the same job for Authors.


Having said that, assuming that you are using one of the high-level languages :) and you're developing a long-living solution I would actually recommend you to use one of the ORMs available for your language to interact with the database. It'll take a bit longer at the beginning, but you'll get a more flexible solution in a long term.