It depends on the conversation – if the conversation starter hasn't checked the "Allow anyone in the conversation to invite others" button when starting it, only they can invite people. They (or you, if it's your conversation) can click "Edit Conversation" above the first post to get to that option to change it.
-
Welcome back to Pokécharms! We've recently launched a new site and upgraded forums, so there may be a few teething issues as everything settles in. Please see our Relaunch FAQs for more information.
Pokécharms
Teapot
Teapot
If you are the conversation starter, or that option is ticked, you can click the "invite more" link under the list of people in the conversation – it's in the sidebar 