Path, a closely watched, generously funded mobile startup, has more users than you might think—but less than it hoped it would have after a tweak to its service.

The company tells us, according to its own statistics, it has reached 500,000 daily users—a number it has not previously revealed.

But publicly available numbers show that the startup recently tried to boost those numbers higher—and failed.

A month ago, Path had one million monthly active users who had linked its mobile "personal journal" service to their Facebook accounts, according to AppData, an app tracking service.

Now AppData has it at 720,000.

That's a big drop.

A source close to the company gave this explanation: This summer, Path made a big change to its app to emphasize adding friends via Facebook. Previously, it had encouraged users to invite friends via email and text message.

It got lots of new users, but those users didn't stick around.

You see that in AppData's figures for daily active users: While the monthly numbers went up, the daily numbers stayed stable. So it looks like the new Facebook users just didn't stick around.

A note about AppData: It only measures users who connect their apps to Facebook, so it doesn't capture all Path users.

The company believes AppData is consistently understating Path's user numbers by a factor of four.

But since AppData directly measures Facebook-connected users, the drop in numbers and the lack of a bump in daily activity shows that Path's Facebook push was unsuccessful.

Here's more evidence that the attempt to grow using Facebook was a flop: Path switched back to emphasizing email and text invitations in a recent app update.

The bad news: Path CEO Dave Morin is a former Facebook executive. And Path has done some bleeding-edge things with the way it app integrates with Facebook. For example, it posted photos natively into Facebook photo albums well before other photo-sharing services like Instagram added that feature.

With all that, you'd expect Path to be really good at integrating with Facebook, whose executives and designers reportedly envy the app's elegance.

Here's our theory: Most Facebook users don't need Path. Path limits your friends list to 150 people, which is a refreshing change for hypernetworked tech and media insiders. But the average Facebook user only has 190 friends. So Path just doesn't feel that different.

Also, Facebook has gotten incredibly noisy, with all kinds of invitations to all kinds of apps. An app invite sent via Facebook feels impersonal—the opposite of the effect Path is striving for.

The problem for Path is that its user numbers are still low, given the time it's spent refining its app and the amount of money it raised. And while the channels Path has been using to build its user base—email and text messages—are high-quality, they're not nearly as viral as a successful Facebook app can be.

Morin has talked about trying to build Path as "slow company." With its Facebook-invite update, Path appears to have tried to take a shortcut—and got burned.

Here's the AppData chart: