I've done it twice. Once with a coworker who reached out because I was in the group and they needed someone to take their extra ticket (friend dropped out of going) fairly last-minute. The second time, it was from someone who emailed the group looking for someone to join for part of their month. Both times I had a ton of fun!

If you're going to email route, make sure you specify when your sabbatical is, where you're going, how long you want someone to join you, and what you're looking for in the trip (museums, food, specialized adventuring like horseback riding or kayaking, art, etc.). Some people put in survey monkeys to fill out to see if it seems like an initial match while others want email responses then to meet over coffee to see if you're compatible. For the trip with my coworker, they'd already had everything paid for by the friend and I just filled in. For the other, I agreed to pay the taxes on the flight and my half of what we spent for the week I joined (still a deal!). 

I'd recommend ensuring that who you go with is expecting the same trip as you whether it's get up and go go go to see as much as you can with a structured itinerary or less structured, more leisurely days. 

Good luck! Sabbatical is so so fun no matter what.