Cross-promoting your content on various social media sites is a great way to build your audience and drive traffic to your best content. Facebook, Twitter, and LinkedIn are the Big 3 of social media marketing and content cross-promotion, but what about Tumblr and Pinterest? These are the two hot social sites that have everyone talking, and they can both be effective tools to expose your content to wider audience.In Pinterest vs. Tumblr: Which Is Better for Brands, I outline the differences between the two tools as well as the audiences that currently use them. Did you know that Pinterest skews more heavily to a female audience and Tumblr is popular among younger audiences? Clearly, these two sites might not be right for every content publisher, but for some niches, they're perfect.Pinterest is a visual social bookmarking site where users save images and videos that they find online on virtual pinboards. Tumblr is more like a multi-media microblogging tool where people publish images, audio, video, quotes, or text in a blog style. Both sites allow sharing and both offer a method for commenting, although Pinterest's commenting tool is more robust than the one found on Tumblr.You can use Pinterest to share images from your articles and blog posts that link back to your original content. Create pinboards categorized by the type of content you publish. For example, if you write a blog about state politics, create pinboards for images from events, pinboards for specific political parties, pinboards for areas of government, and so on. Get creative in how you repurpose your content to expose a new audience to it on Pinterest.On the other hand, Tumblr is handy for publishing multimedia content. For example, you could publish a full article on your website or blog and then share an image, video clip, or quote from that article on Tumblr with a link back to your complete article for people who want to read it. If you publish a podcast, share an audio snippet on Tumblr with a link to the complete podcast for those who want to listen to the entire thing.It's important to keep in mind that Pinterest is still very new and you still need to get an invitation to use it. Tumblr has been around for a longer time and already has established its place in the online content and social media world. Both offer great opportunities to spread your content, so request an invite or create a free account and start poking around. Both are easy to use and can be addictive.You can get all the details about Pinterest vs. Tumblr for brands on the Sprout Social Insights blog, and you can check out my pinboard of brands doing cool things on Pinterest for inspiration. For Tumblr inspiration, SocialFresh put together a list of 60 brands on Tumblr.