Anywhere you find snowmobile trails you can find others to ride with. The trail systems are built and maintained by local riders who enjoy sharing the experience, so one of the best places to start is by contacting the local snowmobile club. The contact info can easily be obtained by visiting the website or Facebook page of the club responsible for the trails in the area you plan to ride. Another source for finding club info is the destinations page of GoSnowmobiling.org here – most, but not all clubs are listed.
One of the best places to meet new riders is through your local Ski-Doo dealer. They know their customers and many are good friends, and can be a good source of information on local events, group rides and how to meet up with others in your area looking to ride.
Additionally, there are many social media groups that can be joined for each riding area. Normally a rider simply asks the members about riding opportunities and you will discover group events that are scheduled, or can make arrangements to join members for fun rides.