Social media is what you make it. You can tweet about what you had for breakfast and spend your time harvesting vegetables in Farmville. Or you can change the world.

We profile five examples of how social media has helped homeless people, from location check-in applications that educate to collecting diapers to blogging while homeless:

1) YouTube

Homeless advocate Mark Horvath (who we interviewed last week) turned to the simplicity of online video to share the stories of homeless people with his site, InvisiblePeople.tv. Suddenly those people are no longer nameless and voiceless. They have a story.

Horvath’s videos have been seen by millions and this summer were selected to be featured on YouTube’s homepage. Mashable also chose him as one of the top 5 YouTube projects that are making a difference. Horvath helped a homeless veteran get his RV back, given a 13-year-old homeless boy hope and given Elizabeth her first pair of clean socks in two weeks.

2) We Are Visible

We Are Visible continues the theme of empowering the homeless (see video above). This site serves to educate homeless people themselves, teaching them to tell their own story through social media. The site includes instructions for setting up Facebook, Twitter, Gmail and blog accounts to give a homeless person a digital home and a platform to share their story.

Launched by Mark Horvath—let’s face it, he’s the prime example of using social media to fight homelessness—the site has become a rallying cry for homeless people. It gives homeless people a voice and a face, allowing them to reconnect and rebuild their lives.

Learn more about homelessness and social media from the book Open Our Eyes: Seeing the Invisible People of Homelessness. It’s inspired by Mark Horvath’s work, includes a profile of Brianna Karp and benefits the nonprofit InvisiblePeople.tv.

3) Foursquare

Abandoned warehouses, dumpsters and old construction sites are showing up on the Foursquare location check-in application in Durham, N.C. It’s an effort by the nonprofit Urban Ministries of Durham to raise awareness about homelessness in the city and was recently profiled by Mashable.

Users will stumble across the locations in the “nearby places” section of the app and will find helpful tips and facts. The idea is to unsettle users and expose their friends and contacts to the issue.

4) Girl’s Guide to Homelessness

In 2009, 24-year-old Brianna Karp ran out of options and found herself sleeping in a trailer in a Walmart parking lot. So she started a blog. She launched GirlsGuidetoHomelessness.com to share her story and maintain some sanity.

The platform attracted attention and she landed a low wage internship with Elle magazine. Then she scored a book deal and her memoir, The Girl’s Guide to Homelessness, releases in May 2011. It’s not a quick path to success and fame—she’s still homeless—but it has given her a path forward and a platform to help other homeless people.

5) Help a Mother Out

Two moms were moved in the midst of the recession by stories of homeless families. The simple lack of diapers got their attention. Food stamps and assistance don’t cover diapers and they become the single greatest need for shelters and homeless families. The two moms set up a blog and started spreading the word with Twitter, Facebook, old school list servs and anything they could think of. They started with $100 and collected 15,000 diapers. They turned Help a Mother Out into a continuing effort and today have collected nearly half a million diapers.

“We may not be changing the world,” they say on their site, “but changing diapers is pretty important too.”

6.) Be Remedy

Be Remedy (@beremedy) is a non-profit organization connecting people who need help with those who want to give it via social media. The idea is that most people would help if they simply knew the needs in their local community. Through applications like Twitter and Facebook, beremedy alerts people when someone in their community needs help. Members then respond to the message or pass on the message to those they feel can. The site says 113,000 people and needs have been met.

Tell us who you follow through social media who’s making a difference.