It might be an idea to try and suggest a social on the WhatsApp group and to see if people are interested. It could be as simple as going to watch one of the big rugby or cricket matches or going bowling. It then gives you the opportunity to meet a few people from the WhatsApp group and (hopefully the person you want to meet) in a group setting. It means that you if you do meet and get on really well then that's great, but if you don't then there's other people you can talk to. It also a more relaxed way of getting to know someone.
A private WhatsApp message from a stranger in a society chat might feel slightly uncomfortable. I think if they had at least met you it would feel less strange, but even then I would wait until they messaged you or until you had chatted or hung out a few times.
Hope that helps,
Oluwatosin – 3rd year student – University of Huddersfield