Worried about an elderly neighbor

I was hoping that someone on this board would have some advice for me. An elderly tenant in my building has been wandering the halls, ringing doorbells at various times of day, and asking for help. She seems to be suffering from dementia and is often confused. I know that she does not have any children who help her, and depends on an elderly brother to help her with grocery shopping. Our building does not have any special services or accommodations for seniors and I am worried about her living alone. Are there any city organizations or agencies that can help, that you would recommend for me to contact? Thank you, in advance.

First try to involve any family members or friends that can be contacted.   

If that isn't possible, contact Adult Protective Services.    They will also try to reach out to anyone who cares about her and assess the situation:

http://www.nyc.gov/html/hra/html/services/adult.shtml

I'd also add make a log of every time she wanders around and what kind of help she asks for. This information could help any caregivers understand her situation more thoroughly. 

Definitely reach out to her brother. Newguy makes a good point too.

It breaks your heart to watch someone go through this

My mother wants to continue being independent but she also struggles with memory loss at times, so she was able to get a home health aide to come to her and help with groceries, reminding her of appointments, etc. Perhaps that may be an option. They can be found through 311 or a google search, and medicaid/medicare and other insurances pay for it.

Also, some seniors who struggle with memory loss have found that they can pay a bit extra to their phone company and it gives a gps/tracking thing where they can call anytime and the person answering will help them to get home, and family members/friends can always find them (as long as they keep the device/ or phone on them at all times, like attached to them. I'm not explaining it very well, but it does seem to help people who struggle and are worried about memory issues.

She may just be going off her meds at random, believing she does not neeed them. Call  for help if you cant get her church or family involved.