If you are talking about flying your friends around and cost sharing then there should be no problem with that. If you are talking about advertising for pleasure flights, even though your not making a "financial" profit" then thats definately a no no. Firstly you would need a CPL and some sort of insurance to cover your passengers.
Remember in this instance, you are still running a commercial enterprise.
many on here will prob have more knowlege and experience than me in this subject, but im sure thats about the size of it.
Hughesyd