On a Tuesday afternoon in downtown San Francisco, a man is sprawled out sleeping on flattened cardboard boxes outside a closed-up building painted black with yellow trim. Pigeons pick at curbside trash near a historic plaque marking 220 Jones Street as the "Screening Room," where they showed the nation's first hard-core pornographic film in 1970 "with landmark success."

The defunct theater is situated in the heart of an area called the Tenderloin, now dense with adult entertainment, liquor stores, and residential hotels. For decades, this 35-block stretch has held a reputation for trash-strewn streets riddled with crime, prostitution, and homelessness -- more than 6,000 are said to live on Tenderloin streets.

But just two doors down from the Screening Room, children in crisp burgundy and black uniforms run in and out of a white storefront entry with a bright yellow sun painted on the window. The building is home to City Impact, a Christian organization founded by Roger and Maite Huang. For 29 years, the outreach has provided food, first aid, thrift clothes, and a K-8 school to those living in the Tenderloin.

Now, with the help of best-selling author and pastor Francis Chan, the Huangs have recently expanded their mission to bring "spiritual awakening and transformation" to the city's worst district. Last November, Chan and the Huang's son Christian launched Adopt-a-Building, a program aiming to establish congregations of believers in each of the area's nearly 600 apartment buildings.

Sean Brakey leads one Adopt-a-Building team of six to the Jefferson Hotel, a government-subsidized housing complex on Eddy Street. They bring bags of donated Trader Joe's groceries to the complex almost weekly, dispersing down narrow halls, and knocking on as many of the 111 doors as time allowed. They have also held bingo parties and recently hosted a banquet dinner in the hotel's basement. Today, Brakey holds a lengthy conversation with Jack, a man in his 50s who eagerly asks questions about the Bible, then tells Brakey to talk slowly while he takes notes. Other residents happily receive the groceries, but not the gospel message.

Adopt-a-Building teams hope to go further: "We're not here just to give handouts. We're here to make disciples," said Chan, author of three New York Times best-seller books, including Crazy Love. In 2010, he resigned as founding pastor of the 4,000-member Cornerstone Church in Simi Valley, Calif., to rethink "how we do church." Last year, he moved to San Francisco with his wife and five children before joining City Impact.

Instead of building a large congregation here, Chan and his team aspire to "take the church to residents of the Tenderloin, to where they live," and to eventually raise up leaders who can run "home churches" in each of these buildings. So far, most of their work has been one-on-one.

City Impact workers and volunteers use a curriculum Chan and Christian author David Platt recently developed called "Multiply." The free online discipleship curriculum is part of a broader effort by Chan and Platt to provide new believers and lay members of the church a starting point for growing in their faith and sharing the gospel. Already, City Impact workers have begun to take a handful of recently baptized residents through the tutorials that cover topics like "Living Like a Disciple," "Studying the Bible," and "Living as the Church."

Chan's involvement has brought national attention to City Impact. The group now prepares for its second annual City Impact Conference, with Chan as the keynote speaker, meant to inspire believers to reach their cities in a similar way. As word gets out, dozens of church and school groups are coming to volunteer for short-term mission work.

Still, Adopt-a-Building teams encounter challenges specific to inner-city missions -- in particular, residents battling deep-seeded addictions, apathy, and an entitlement attitude.

At a recent Tuesday morning meeting, Chan encouraged staff workers and interns crowded around a conference table cluttered with laptops, bags of croissants, and a giant bowl of peanuts. When residents "give their lives to the Lord apparently, but then go right back into their sin...It's not wrong to want them to repent," he tells them. "But we can't worship revival more than we worship Jesus. God never promised us revival. He promises persecution. He promises people walking away from us. But he also promises his presence will be with us as we go and make disciples."

Similarly, Roger Huang notes the tagline for City Impact is "changing one life at a time."

"We always want to have a quick result where 500 people were saved and all were transformed...People aren't always transformed in one service or one class, like the church sometimes wants us to believe," said Huang, who regularly takes teams on prayer walks through the Tenderloin neighborhood. Since they started praying over the city blocks, a liquor store and a strip club near their school has closed.

"We have the most liquor stores, underground pot clubs, strip clubs, and porn shops in San Francisco on these blocks. The battle doesn't end, but we believe we have been placed here as a point of light in a dark place."