Maybe you’re not trying

> I learned his real name and used it to track down an old friend of his to ask for help

Does anybody else find this strange? There's this person whose name you don't even know, but somehow you know who his old friends are? This is not a situation I'm familiar with.

It doesn't sound that far-fetched. The stalker probably told her that he was planning to join her company and meet her, which gave her enough information to find his name. Once she had his name, she could find his profile on social media and see who his friends were.

> > I learned his real name and used it to track down an old friend of his to ask for help

You left out the adverbial phrase. The whole sentence is

> When he reached out to my company six months later to apply for a job, I learned his real name and used it to track down an old friend of his to ask for help — but the friend told me he was afraid to intervene because he didn’t want to become a target himself.

When the stalker applied for a job, additional details may have become available to the OP, potentially including personal references (i.e. "old friend".)

I think the old friend is _her_ old friend, not the stalker's.

The sentence is a bit ambiguous but that's what seems to make the most sense to me.

"old friend of HIS" is not ambiguous.

It clearly says "an old friend of his"

There's probably more to the story than the author is willing to let us know, but that wouldn't have made for a nice Silicon Valley "you can do it if you really want it for real!"-success story.