It depends on what you mean by 'similar to facebook'. Facebook has several overlapping uses. For example:
1 - staying in contact with friends and family, posting pictures of your children or cats, which some people have said is all they do.
2 - announcing gigs at a folkclub, posting reports of gigs, maybe coments from those who attended (or maybe not allowing comments).
3 - promoting your political party, seeking reaction.

Facebook has built its business on linking those and many other functions together, to keep you 'engaged', find out as much as possible about you (and selling that data), and thus to drive advertising revenue - be that products, or political messages.

Decide what you value facebook for, and more importantly what you dislike about it or think is socially divisive about it. Then type 'alternatives to facebook' in your favourite (unbiased) search engine. Examine who owns or runs these services.

For #1 - staying in contact with friends and family - you then face the biggest problem - persuading your friends and family to use it.

I have relatives who are all 'on facebook'. When I tell them I'm not they're very surprised; they don't see anything wrong with it. Or maybe with their use if it.

My particular beef is with folkclubs, say, who decide they ought to have a facebook site, but don't set it as 'public' - maybe don't even know that's possible. They then allow their website to fall into disuse.

This, in yesterday's Guardian is insightful I thought:
Social media fuels narcissists’ worst desires, making reasoned debate near impossible