Nextdoor.com has worked really well for my neighborhood of more than 800 homes. People use it to organize groups and activities, play groups, find babysitters, post items for sale, report suspicious characters, lost pets, car break-ins, service recommendations, etc.
The nice thing is that it is only for the community you define, so people participate more than if it were used by an entire town. It's a great concept. A lot of burglaries in our neighborhood have been solved, and lost pets returned home.
After the snow/ice storm in Atlanta last week, people were offering rides to neighbors to go pick up their abandoned cars. We have a very organized effort to catch, spay/neuter feral cats and return them to the neighborhood - all organized on NextDoor.
Can't say enough great things about it! I think it would be a great way to get a community rolling for you...