Couchsurfing is great- there's a huge community and people love to meet travellers. Be extra careful about people's reputation and if they have been vouched for, because there tends to be a lot of older men using the website to meet foreign women. Other than that caveat, you'll find the community is super active- they meet every other week on alternating sides of the city.
Oh, and just because of the city's size- try to avoid staying in any places that require too long a commute to get to the center where you'll spend most of your time.
