Sites like now.gg often host mobile games that can be played in a browser. Check if IMVU is available there; these cloud gaming sites often slip past school filters because they are categorized differently than social media sites.
If you are allowed to install extensions on your browser (or if you are on your own device on restricted WiFi), a simple VPN extension can mask your traffic. Note: Be careful, as some schools flag VPN usage. imvu unblocked
