I am using an HTTP proxy server to connect to the internet.
Because of that my pings are not working
says Unreachable Host
How can I configure
ping to use the HTTP proxy?
In general you can't.
ping needs a direct network connection on the IP level to do its work. A proxy works on a higher layer of the TCP/IP network model, where there is no direct access to the IP protocol.
You would need to somehow circumvent the proxy (change firewall settings, use a VPN, ...). Whether this is possible (and allowed) depends on your network configuration, but it's probably not possible.
As a workaround, there are many web-based ping services available (search for "web-based ping"). These will work.