I haven't seen any Gamblig Platform who used Telegram for Promotions, most I know is that they use Discord.
Do you have any Idea why they don't have any Telegram Communities? and why does it seem they don't use this platform for their promotions?
TL;DR
I am not sure about others but stake.com always offer their promotions through telegram or shall I say they announce their promotions via telegram because our weekly bonus is sent through telegram and then we have all the notifications like the daily challenges are announced via telegram only apart from the random drops that are only sent via telegram.
Yes they don't do any telegram giveaways such that they have a group or anything but that might be because if they make a community and add players people will spam each other blatantly and high rollers will have a tough life ahead of them being bugged with messages/calls and maybe even threats because everyone wants to juice money out of them.