I have the Riverview content for my Sims 3. However my issue is when I download it, and manually install it (by clicking the icon in the sims launcher)... after it says "installation success" I go to run the game. It loads... but when I go to new game, and go to choose a town, it's just not there. So I went back to check the sims launcher and Riverview is no longer in the "installed" area...just gone.

I've reinstalled it many times, but Riverview just continues to remove itself from the installed section. I've looked online but no one seemed to have my particular problem...

Is it just Riverview, or other sims3packs too? When did you download Riverview from the Store? This is a very common problem with sims3pack content, there's no definitive fix but there are a few things you can still try.

Just Riverview. I DL'd it today, though not from the store as I don't have/don't know the pin, however the post said it was from there. (I've heard that many people are having problems with the direct Sims Store Riverview as well)...

It could be a problem with your DCCache files- test this by dragging your Documents/ Electronic Arts/ The Sims 3 folder to the desktop, and then copying Riverview to the Downloads folder and installing with Launcher again.

If that doesn't help then it could be that the Riverview Sims3Pack you downloaded is faulty. If by 'Pin' you mean your Sims3 site password, then I think you can tell them that you forgot your password to get it reset. It's best to get a fresh download off the Sims3 site, as any you download from elsewhere will probably be compressed or otherwise changed.