Our street has a Facebook group, it helps us organise events (and vote for winning wings), coordinate meals when people are sick, arrange pet minding and bin duty when people are on holidays, and serves as a modern version of Neighbourhood Watch when things go wrong (and they do). This, alone, is a good reason to create such a thing and invite your neighbours to join, but like the first point it lends itself to the next...
3. Build some traditions
We do birthdays, random hang outs and spontaneous working bees, but these bigger events are a good way for new people to dip their toes in because they tend to have a more visible presence and we normally letter box drop to invite people along. They become part of the rhythm of life together and build community through the stories and memories they create.
"Love your neighbour" — Jesus (he was a pretty influential guy who maybe knew some stuff).
Here's a post I wrote a while back on my blog with some more info about how #lifeoncurfew unfolded, and more about why you should do this with your neighbours. It'll be good for you.
Our weird modern individualism leaves us shut in, buffered away in our little castles, where we're hypnotised by big screens, binge watching streamed shows that our friends aren't necessarily watching... and that makes us feel isolated and lonely. Maybe you need to get out more and maybe that starts with opening your front door.