There are many off-page SEO techniques which help to build quality backlinks for your site. Below are the list of websites which can help to boost your search engine ranking...
https://linkedin.com
https://quora.com
https://medium.com
https://tumblr.com
https://academia.edu
https://wordpress.com
https://blogger.com
https://behance.net
https://evernote.com
https://steemit.com
https://weebly.com
https://livejournal.com
https://pearltrees.com
http://apsense.com
https://storeboard.com
http://www.pinterest.com
http://www.reddit.com
https://mix.com
http://soup.io
http://pen.io
http://hubpages.com
http://diigo.com
http://plurk.com