wp_ajax_bbp_suggest_user

See hook in action

See this hook used in plugins:

Select Pluginbbpress.2.5.14bbpress.2.6.0bbpress.2.6.1bbpress.2.6.2bbpress.2.6.3bbpress.2.6.4bbpress.2.6.5bbpress.2.6.6bbpress.2.6.9