I completely understand, it happened to me all the time.
What helped with me, was staying quiet for a while and observing how the conversation 'flowed' so where would be 'acceptable' for someone to chip in, and *how* things were said amongst that group of people. It also helps, to try and talk to one or more of them alone outside group conversations, when familiarity is built with one, they tend to notice you more, and then as you become 'noticed' the others start doing so, and viola, chain effect. (Especially better to do this with the 'louder' ones.)