It's the rare writer today who doesn't have at least some contact with other writers online -- through Facebook groups, subject matter forums, or dedicated category organizations. Places where writers gather online, from tiny five-member Facebook groups to the Romance Writers of America, all have the same basic goal: to encourage writers and help them to improve their writing. These can be more or less effective, depending on your participation, but there's still something to be said for meeting other writers in the flesh. If your online friends are the only ones seeing your work, maybe it's time to find the advantages in a real world writers group.
Social Aspects
Admit it. Whether you write full time or just do it as a sideline, you sit in a room alone while writing. It's your solitary activity, rarely shared with the people in your life. Why not turn your writing into a means to improve your social life? If writing groups are anything, they're filled with people who have one thing in common: writers. The odds are good that you'll find a few you like, and getting out of the house to enjoy yourself while still working on your book is the best of both worlds.
Motivation
Most writers groups include readings and critiques of each others' work, on something of a rotating basis. Whether your group has everyone read a short passage each week or you rotate on a weekly basis, it will give you a powerful motivation to get your writing done every day. It's very easy to slide out from under online obligations with people you'll likely never meet, but with real people in your neighborhood, it's a much stronger commitment.
Honest Critiques
The ability to be anyone and say anything online is one of the charms and hazards of the digital world. Online critique groups can be useful, but it's very easy for people to pile on, either in praise or in criticism. There are no consequences for any behavior in those groups except the bad opinion of others you'll never meet. A live group, on the other hand, is a social being. Members get to know each other and, even if they're not all friends, they at least respect each other enough to be honest about what they say. It's much harder to lie about your opinions to someone face-to-face, and impossible to be a troll, as some people become online.
Create Your Own Group
Creating your own group is the best way as a self published author or writer to make sure you get what you need out of it. Determine what you want from the group (encouragement, advice, critiques, challenges), then find other writers who have the same needs. Meet-up is a successful service online that allows you to post open invitations for real world meetings of every type. Set your meeting in a public place such as a coffee shop or restaurant, and keep the Meet-up page current to constantly encourage new members.
Keep the Faith and May the Force be with You!