An old unconnected htc one x+ recently stolen
The short answer is... maybe.  Did you have a pin or pattern set on your phone to prevent anyone from opening it?  If you had something as simple as a pattern lockscreen or a 4 digit pin, it's highly unlikely (although, not at all impossible) that anyone is going to invest the time and effort it would take to break that security.  If you left it wide open with no sort of lockscreen protection, then anything you have saved on that phone is open game.  If you saved logins through apps on your phone... all they would have to do is connect to wifi and have access to whatever apps you have saved logins enabled for.  Your google account, at the very least, could be compromised easily (since they already have access to it- I feel certain if you're worried about this then you dont have 2FA enabled). I would recommend changing password to any services you used on that phone as a precaution, especially if you didn't have a lock feature enabled.