The last update for RAW was in December 2013. More recent cameras are probably not supported unless they use the DNG format.
The problem with RAW is that the camera makers generally create a new, distinct (and incompatible) raw format for just about every new camera body they make. That means, for example, that a .CR2 raw from a Canon 20d is not at all the same as a .CR2 raw from a Canon 5D, or the latest Rebel. They all have the .CR2 extension. But they're incompatible and different. The same is true for the RAWs of other camera makers.
This means that for every new camera Picasa needs to be updated to support it, and sadly Picasa has not been updated for RAW since Dec. 2013, so RAW files for more recent cameras won't be supported. The camera brands and RAW extensions Picasa aims to support are listed here: https://support.google.com/picasa/answer/15625
Adobe created an "open" RAW format, DNG, that doesn't have the above problem. You can convert your pictures first to DNG using Adobe DNG converter, and Picasa should show those properly:
Two interesting articles about DNG vs RAW:
https://photographylife.com/dng-vs-raw
https://photographylife.com/why-i-no-longer-convert-raw-files-to-dng
Some lenses that have the advantage that they are very compact for the given quality create a lot of distortion in the image. Some cameras correct this in camera when shooting JPEG, but RAW may still be distorted. This distortion can be solved by using fancy software to convert the pictures to jpg before you can use them in Picasa.
Some more info about this can be found here: http://www.photographerslounge.org/showthread.php?t=13800
Picasa's main goal is in making it as easy and fast as possible for anyone to organize and edit their pictures.
Specifically for RAW pictures, this is accomplished by doing a fully automatic conversion of the 12 or 16 bit RAW data to 8-bit with no input from you. This way, you don't even see a difference in how you work with them. You can see the photo and edit just like you would a JPEG. Or burn it to a Gift CD, upload to a web album, email it to someone, or print it. It's easy to work with and is exactly the same as if you were shooting JPEGs. There is no tricky stuff to worry about. This approach is great for 95% of the pictures of 95% of people... and so it maps perfectly on the goal of the Picasa developers.
But... if you want to use the full potential of RAW to get the best result you'll need to use a "real" raw processor, so you can unlock the real power of RAW pictures by choosing the color balance,... yourself. On well-exposed, well-lit pictures the difference will be relatively small and not worth the effort (for most people), but on the tougher shots like eg. evening/night shots or shots with shady areas,... taking full control can give a huge difference and may/will be worth the extra effort. Examples of applications that give you more control over the conversion are:
Raw Therapee (free): www.rawtherapee.com
Adobe Lightroom (not free): www.adobe.com/Lightroom
And after the fine-tuning you can just save them as a JPG on a location Picasa will find the picture... and you'll be able to use the power of both worlds...