Funnily enough I was in Lisbon a few weeks ago talking to some TEFL people - fantastic city and great food!
But to jobs... most jobs are found through either local advertisements or word of mouth. The start of the school year is the best time to find work there so that means at the end of Summer (although of course if you're there now there's no harm in contacting all the schools and letting them know and then getting back in touch again at the end of Summer).
So I'd suggest getting the Yellow Pages and finding every single school and visiting them on spec and leaving your CV with them. Also you could check with the English language bookshops where job ads are occasionally posted.
More on teaching in Portugal