Homeless citizens wait outside a homeless shelter

Having worked with many people who just left homeless shelters in my community service, I have noticed how hard it is for many who don't have a place to live.
This article on CNN advises readers on what to do if they see someone who appears to be homeless in a hostile situation, or if they clearly need medical attention. They say that most major cities such as San Francisco and New York have hotlines you can call. Otherwise to just call the police.
Also, when you see a homeless person asking for money:

"We don't really promote giving people cash money," said Deronda Metz, director of social services for the Salvation Army of Charlotte, North Carolina. "If you have a blanket, that would be great. If you have food to give, that would be double good. We don't promote giving people a ride."

For more information on what you should and shouldn't do, check out the full article.