If I had to execute a way to get new players into tf2 and grow the community I would create a league that is:
a) free
b) has a large cash prize
c) only new to comp tf2 players can play in, no esea people. (that way the teams don't get raped and give up and quit)
d) Advertise to pubbers and everyone who's new or wants to get into comp tf2 about this league and assure them the skill level is for new players only.
You have to give people who want to get into comp tf2 some kind of goal like winning something at a level they are capable of winning it at.
Assigning these new teams mentors through out the season to sit in on like a scrim a week wouldn't be a bad idea either. That makes it a competition to see who's the best mentor also lol, maybe the mentor can get a piece of the cash prize to.