If you want to create a group to inform about promotions then I would guess your best option is to adevrtise in the site.

Anyway, first approach would be contacting the mods

http://www.qatarliving.com/contact

And the second approach is to request information on how to advertise in QL

http://www.qatarliving.com/advertise

Yet another chance is to post classifieds under the services or for sale/wanted categories.

Regards!!