I'm looking for quite a thin font that is save to use in regards, to website users. Any suggestions for a save font stack
Check out Google Fonts. That's a good place to start to find nice web fonts of all sorts. You don't need to worry too much about stacks, then, as most if not all users should get the font you want.
Also if you don't use Google Fonts, make sure that you select at least 3 font types, 1 for Windows, 1 for Mac and 1 for Linux, as many font-types are only available for a specific OS. Of course there are fonts that are common to several OS, but they are few.
Google fonts should give you all the fonts you can use. Otherwise, just use Arial, I'd say that's the most common and also quite thin
For usabilty's sake, they suggest to use verdana, which is easier for visitors to read