Cross promotion has worked for a lot of people. In most cases it is used to get more people to view what one has posted. However, it is also a good avenue to gain followers from instead of using free followers. Cross promotion is where one posts an image or a status on one platform and shares it across other platforms. This often works with twitter, instagram, Facebook, Flickr, tumblr and even Foursquare. Once people see the post, they will strive to follow you on the original platform it was posted and this increases your followers.
Linking the accounts also works as the platforms will always prompt you to follow people who are on that platform and are your followers in other platforms. This eventually increases the number of people that follow you. Unlike free followers, it allows you to have followers that are responsive and can express their opinions of what you have updated. It also increases your online popularity which is the overall aim of having many followers. You can also embed the posts that you cross promote such that people are promoted to visit your account in order to get more information.