OK, so the park isn't officially the home of a running club, but members spend so much time at Mine Falls Park that it's sort of home-away-from-home.
If you have avoided the Mine Falls area out of concerns for personal safety because it's an urban park, you might want to try the trails late in the day on Wednesdays between now & October. Gate City Striders (GCS) use the park and the adjacent NHS-South track for weekly workouts at 6 p.m., giving you plenty of company on the trails for an hour or so. You can park in the Nashua High School-South lot, behind the school, near the track.
By the way, I've used these trails for years, in all seasons, at all daylight hours & occasionally at dusk. I have not been accosted at any time. The creepiest near-encounter I had with a suspicious-looking character was in the east end of the park, behind the now-renovated mill buildings, a decade ago when they were still pretty derelict. The character disappeared as soon as a group of half a dozen Striders came into view on their Wednesday run.
I'm responsible for my own safety, so of course there's risk, which I try to mitigate by carrying assorted devices. I usually let someone in my family know where I'm headed. I actually feel more at-risk in urban parks than on remote trails. I don't let the risk scare me into staying home.
Come check out GCS in any case. Fine folk, in my experience.