actual facts or just rumor?

The official Mountain View Police Department Twitter account says they have responded to incidents, but they are not disclosing details at this time. Everything else I've heard is "my co-worker is in the hospital" or "my neighbor had surgery" etc.

I really appreciate the apparent intent of the posting, but MVPD is pretty good about releasing crime warnings when something serious is happening -- whether or not they also give names of victims or suspects (often not). "Possibly because the teenagers are under age" is speculative, and a weak explanation for lack of corroboration from MVPD. Who maintain a Nixle service for that, and post frequent bulletins on social media.

Also: One telltale of the difference between real journalism and careless blog posts is that journalists describe what they know (like, "most of the alleged robberies" if they've heard a report or claim) rather than what they assume ("most of the robberies"). Another difference is that the journalists sign their own names, if they want credibility.

Every time I hear about this the story gets bigger, so I'm a bit sceptical.

First I heard it was "A college acquaintance reported that her brother-in-law was attacked while riding home on Stevens Creek Trail ", and now it has grown to "gangs of teenagers robbing multiple victims".

mvpd said it was a pedestrian/bicycle collision. Time will tell what the deal is. I'll keep using the trail.

Only 4th hand reports of this happening. I've seen zero reports that this is anything more than a rumor. Nothing has been reported by the MVPD, even when directly asked. Might be worth keeping an eye out for punks though