@comamy You have mentioned that they already have a presence on social networks, so my suggestion is first to friend them, then build a relation with them thru their social network pages, comments, then a compliments, then after getting to know them go a head and tell them that they need to improve their social network pages and also tell them that you can help them, I think that will be way better because, because people usually say yes to someone they already know rather then a person that they have never communicated with,
I hope that will help. Good luck