There are a number of active sites where gainers and encouragers socialize. Most require joining as a member and membership is often subject to verification or approval of some kind. All offer free accounts and some offer premium services for paid accounts.
Please note that these are not pornographic sites and they are not open to underage users. They have strict rules about the kinds of content that can be posted and they do not allow underage users to participate.
http://www.grommr.com | The most popular of the social networking sites for gainers and encouragers, grommr has profiles along with a more sophisticated newsfeed system and advanced search capabilities. | |
http://www.feabie.com | A variation of grommr that is intended for heterosexual gainers and encouragers. |
For a less gay-oriented site, try http://www.fantasyfeeder.com and for a chub/chaser oriented site, try http://www.biggercity.com.