Without clear guidelines from the books, we are left to to try to find the best interpretation our self. I'd say that these non-aoe spells/spell-like/supernatural/extraordinary abilities that do not require an attack roll would affect the character. That is my RAI take on it.
Trying to get a RAW reading:
When using a tower shield in this way, you must choose one edge of your space. That edge is treated as a solid wall for attacks targeting you only. You gain total cover for attacks that pass through this edge and no cover for attacks that do not pass through this edge (see Combat). The shield does not, however, provide cover against targeted spells; a spellcaster can cast a spell on you by targeting the shield you are holding.
The CRB brings up attacks a lot, so a strict interpretation could say that it effects and only effects anything that is rolling an attack to hit you. (this has it's own problems when someone tries to sunder the shield, but it works for spells.)
It seems fairly clear that the shield provides cover against physical damage, but does not protect the wielder from being targeted by magical effects because they can just target the shield to get to the person holding it.
But would protect against Acid Arrow or Disintegrate because those are attacks targeting you, opposed to Hold Person that is a targeted spell.