Sharetivity is one of 65 companies chosen by VentureBeat to launch at the DEMO Spring 2010 event taking place this week. These companies do pay a fee to present, but our coverage of them remains objective.

With Facebook users sharing more than 5 billion pieces of content a week, it’s becoming clear that people are finding more photos, articles and videos than ever before through friends.

A Palo Alto-based startup called Sharetivity is trying to tap into that. It simultaneously shares content to all of your social networks and selected email contacts, while bookmarking it at the same time. It’s like social bookmarking service Delicious but aims for a more mainstream audience because it rests on top of powerful existing social networks.

The startup uses a browser plug-in (which may present a hurdle for new users) that lets people select multiple pages and share them with one click. They can pass content along through as few or as many social channels as they want. There’s also a discussion board where you can comment on shared items from friends.

While there might be a small subset of users that want to organize and save their shared content with specialized services like Sharetivity, Delicious, or the very visual French startup Pearltrees, I suspect that a mainstream audience may want to stick with existing basics like Facebook. Browser plug-ins are also an extremely difficult approach because you have to convince new users to go to your site, install the app, and then actively use it.

The company has raised angel funding and hopes to secure marketing partnerships to bring in revenue.