I manage the Nextdoor site for Seward Park and if you live in that area, encourage you to join. Nextdoor was founded by the guys at Zillow and acts as a neighborhood portal to connect neighbors, post items for sale, recommend local retails stores, post events, whatever.
They limit how many people or households can join and restrict it by area. If you fall outside the boundary I encourage you to form a new site for that area, i.e. Rainier Beach.
Take a look and sign up at Nextdoor dot com