1. Use RSS feeds from Twitter/Facebook to constantly post new threads/posts in a subforum. Give Google your sitemaps. Twitter/Facebook content/users are not being indexed on Google. Given that, it's your duty to do it.
What is your new forum-based site? Categorizing social media. That is how you are legit.
2. Google+ SEO. You can auto post to Google Profiles using THIS technique (no one is automating this yet):
Basically, you Automate this using a RSS to Email through SMTP (RSS to Email to Google Voice to Google Plus) . This will auto-post an RSS feed to your Google+ profile. Given the image below, I believe you will see how it will be lucrative to have a Google+ profile that has a lot of content (there is a greater chance for Google to list you on the Search Engine).
Edit: I was meaning for it to say "Receive" in the title.