I use the flybys option of Strava and add people who run my same routes. My profile is public and I share pictures and interact with friends, so hopefully it’s not weird for people to see me following them. Anyway, most follow me back and then we start commenting on each other’s run and eventually have ran together. I love the option, but understand the first online interactions can be a bit tricky. Guess it’d be easier if you have a history of running on those trails and publish your runs with a ‘anybody wants to join next time?’ message. Good luck! :)