Unfortunately I think it's just going to take time and being willing to continue to contribute to the tribe yourself. I'm currently hoping more people will start contributing in /t/writingprompts because I find it fun trying to tackle some of them. But it's just going to take more time as people other become more used to posting or as more people join.
Showing passion for your tribeike you are doing and keeping the posts flowing I think also will help you. Remember the tribe you have here will probably draw a lot of shy people as well which means they will take time to feel comfortable responding even though it's anonymous.
Unfortunately I think it's just going to take time and being willing to continue to contribute to the tribe yourself. I'm currently hoping more people will start contributing in /t/writingprompts because I find it fun trying to tackle some of them. But it's just going to take more time as people other become more used to posting or as more people join.
Showing passion for your tribeike you are doing and keeping the posts flowing I think also will help you. Remember the tribe you have here will probably draw a lot of shy people as well which means they will take time to feel comfortable responding even though it's anonymous.