This has been discussed quite a lot recently. A lot of people are relucatant to put their time and effort into a promise of a return, whereas others are willing to invest in a future percentage. Depending on what you need doing you might be better off posting on a freelance website just for some paid help at the moment. Get a feel for the person doing the work for you and then possibly approach them with the idea of a partnership if they seem interested enough. Personally I wouldn't go straight into offering a percentage of the potential profits when there are other ways to get the work done. Just my opinion though.