This is primarily a fundraising activity but does bring the added benefit of being great for team building and helps your young people get to know others in the group.
A worker auction basically involves auctioning your young people (and leaders) off as workers to the highest bidder.
Start by getting a list of kids and leaders that are willing to auction themselves off. You can group some together if that makes them more comfortable... or more sell-able! :)
For each person (or group), get a list of tasks they are willing to do (for example, gardening, cooking, cleaning, etc). If your leaders have a trade they do as a profession, make sure that's listed (graphic designers, painters, etc can fetch a lot of money!).
Schedule a night a month or so in advance to auction everyone off. If you can, publicize the list of kids (and tasks) in advance so people attending can plan their 'purchases'. Make sure in your publicity that you specify where the money is going - if it's a good cause it encourages people to be generous. They key is making sure this night is well attended by parents or others from your church or group, as they are the ones that will be doing the bidding.
Setup a cat walk so those being auctioned can come out and strut their stuff in front of the crowd. Have music, lights - anything to set the atmosphere. Make sure you get a charismatic MC and auctioneer - it's important they encourage those attending to bid high. This person is key in keeping the night entertaining.
Encourage the kids to be creative - for example we once had one group of five kids create a package which they titled "have a hot date at home". It involved them coming around to your house, cooking the winning bidder a meal, setting a table with candles, and serving dinner. One was a violinist so she played music in the background during dinner. They dressed up formally and made it a great night. The kids did the washing up at the end of the night - the couple that won the bid were rapt!
If you can convince the senior minister to offer their services, they often fetch a pretty high price in the auction as well!
Note: Just to explain the context of the comments below, this was originally titled "Slave auction" but was changed to avoid offending anyone.