Hello,
I suggest you to go with wordpress CMS and following is the reason why?
For wordpress social network my suggestion:
There are social networking platform available in wordpress but they are limited as per the functionality they come with but the best thing about them is you can get them setup quickly which I can help you with quite easily with my experience. In wordpress you can do the customization to some extent as per its allowance from the developers of that particular theme and if you make a wordpress social network platform from scratch it will be really very much time taking. So my suggestion to you is pick a nice social networking platform as per the urls I mentioned below which suites your need and let me do rest of the job.
For wordpress security I can help you do following:
I will implement a security layer on your CMS as well which helps in whenever anyone tries to break into your website then you will always get notified who tried to breach your site's security and from where & that user's IP get black listed & he got blocked by the system automatically as well and you will always get a notification if there is something wrong with in your site or with any files in it or not. Security layer will also help you see all your traffic in real-time, including robots, humans, 404 errors, logins and logouts and who is consuming most of your content. Enhances your situational awareness of which security threats your site is facing.
Note: I can help you with custo