Welcome to the forum.
I see you're based in Spain. Have you looked at LingoBongo.com? It started as a website for people to find accommodation but it has turned into a huge resource for jobs, accommodation, items for sale etc. When I was teaching in Madrid, I picked up a few students over the summer (2009 and 2010) by advertising there. All of my students wanted face-to-face classes but if you make it clear you're offering Skype classes, you can attract people from outside Madrid and Barcelona.