Established social media presence of Orange County Register newspaper and rolled out social initiative at newspapers throughout the U.S. Also: speaker and coder who built web sites before there were tools for building web sites.
If you plan to create a social network that would be used for roadside assistance, then your biggest obstacle will definitely be competition from existing social network giants. People can currently use Twitter or Facebook to reach out to friends for help.
If, instead, your service will use existing social networks, I think your big obstacle will be ensuring the safety of users. A user will need to share his or her location to get assistance. You have to figure out a way to prevent criminals from taking advantage of that information to find easy victims for theft or worse. Also, criminals could pose as distressed travelers to lure unsuspecting good samaritans into a position where they could become victims. Once you solve that, your'll have to market your service as both reliable and safe.
Good luck to you!
Find people on Twitter who are experiencing a problem that your app can solve. For example, if your app brightens photos, search on twitter for ["too dark" camera] (without the brackets). You'll quickly find people who could use your app. Reach out to them by replying, making sure to express your sympathy, and offering them your solution. With a little work, you can quickly spot "influential" Twitter users, and focus on them, making sure to maintain your relationship with them and sharing their success on your site or through your Twitter accounts. You can use Twitter to convert frustrated people into happy customers, and then share their story with your followers.