It can be difficult to find out if someone is still living but if you have their full name and date of birth you can try finding out at the county clerks office in the city/town where they lived. Having the social securty number will produce better results as you can go to the clerks office or search online. Go to :http://www.socialsecurity.gov/ this may help providing you have the ssn.
You can find out or check if someone is still alive by checking if he is still breathing. You can also check his vitals or pulse for any vibration. If you are still not able to tell. Tap the person or call 911 emergency or ambulance.