Craigslist rooms and shares. You can either post that you're looking for roommates to find an apartment together, or find a 2 bedroom yourself, secure the apartment, and then use rooms and shares to find roommates. The latter one requires more money for the deposit and a landlord who's willing to work with you, but you will get applications. When I did that years ago, I got 50+ emails about the one small room that we had free.

Conversely, the rooms and shares Craigslist can also be useful if you're moving and just want to move straight into an apartment with roommates who already live there. My sibling did this when she moved to Boston last year. She had to email 30-40+ places, which was very challenging, but found a room in an apartment that she really likes.