Best helpers I ever found were hispanic guys, at the corner where day laborers wait to find work. Newspaper ads and Craigslist ads bring in nothing buy lazy slackers, who can never show up for work on time.
Heck,two of my daylabor hires, later became foreman for me as I expanded.
The second best source for me, was high school and college guys from our church's youth dept. They always had to leave too early in the season to return to school though.