You do not need to be able to see Wall of Force to Disintegrate it.
This is clarified by Crawford on Twitter here:
Disintegrate is a mischievous spell. It says you must see its target, then quickly makes an exception for wall of force and the like.
Though it can be interpreted that you have to be able to see it because of the general rule, the intent and by the ruling of Crawford seems to be that you can target it without needing to see it.
This most likely applies to other invisible creations of force that Disintegrate can destroy.
With the wording of "Such as" in the description of Disintegrate it seems to leave a place to plug in spells to see if it would work correctly. As such one could replace "Wall of Force" with "Force Cage" and get the same results. This is also supported by Crawford's statement at the end of "And the like"
If you target someone in a Wall of Force it most likely has no effect, RAW. There is no valid target/path of effect.
Somewhat related: Can spells be cast through a Wall of Force?
Though that is Mearls and not Crawford, so anything you find by Crawford is the real 'rule of God', it seems consistant with other rulings.
It would be an easy/common suggestion to say your Disintegrate hits the Wall of Force and destroys it so you don't wind up losing a spell slot for nothing.
There's another interpretation that says it just flat hits the wall, however.
Still going off of Mike Mearls' rulings, so therefore not completely 100% foolproof, one can find the phrase:
would block physical effect of spell but not mess with targeting that needs sight
This would imply that you could properly target someone in a Wall of Force, as you can see them, but the physical ray of the spell would hit the Wall. Because of the spell being what it is, it should then destroy the Wall of Force.
Because of these two slightly inconsistent interpretations, with both having more or less the same output, I think its safe to say that the Wall of Force is going to be destroyed regardless. The reason this gets slightly 'inconsistent' is that the second answer in this link goes into great detail explaining that by hard RAW you can't target someone who is in Total Cover. It conflicts with the interpretation by Mearls.