How would I use this script?
print(game:GetService("HttpService"):GetAsync("http://rproxy.pw/My/Groups.aspx?gid=2672295"))
To gather a certain part of the website but not all the actual HTML coding it self, just like Group Members.
If that prints the HTML of the page, use string manipulation to find the section you want. Using this page is a good way to see what you'll actually be getting from that GetAsync call.
Your initial link is a redirect, but using http://rproxy.pw/Groups/group.aspx?gid=2672295
gives the actual page.
After a few minutes delving into that HTML, I can't actually find any group member names. So, either this is the wrong page, or using the simple proxy won't help you here.
What are you actually trying to do here? That is, why do you need to get the members of the Group? There might be a better (aka easier to code) alternative than using HTTPService.