When you want to participate in something with others, the phrase "join in" comes to mind. However, there are various synonyms you can use to spice up your language. "Participate in" or "take part in" come in handy, as they give a formal tone to the sentence. You can also use "chime in," which tends to connote a sudden contribution to an ongoing discussion. "Add to" or "contribute to" make for excellent alternatives if you wish to lend a hand or contribute your thoughts without being actively involved. Overall, using synonyms for "join in" elevates your language and adds variety, making it an interesting read.