What user acquisition channels work for local / hyperlocal apps?

As your question was not clearn to my understanding on what problem you are trying to solve I will present some interpretations and how I would approach this:

Geofencing can be understood in 3 manners:

a- People that are inside a certain region

b- People that declare to live on a certain region

c- People that live on a certain region

And by region I will break into 3 different categories:

- Broad - country level

- Narrow - City

- Super narrow - neightbourhood

All mentioned platforms have limitations, but by my experience:

- Fb / Snap (available on selected countries) / Twitter offers all categories of region and all targeting options (that is actually recent) buy you would have a severe CPM increase due to that targeting

- For "a" region targeting I would mention programmatic as an option, with some kind of DMP for IP <> Region conversion. Of course for that targeting Super Narrow can be imprecise

- If your problem is broad targeting pretty much any advertising network can solve that

- Apple search use broad targeting and "b" targeting

- Google uses "a" and "c" targeting (but you can't differentiate) and can be pretty narrow on targeting location

Hope this helps

Depending on your customer demographic and geo, Nextdoor is another channel to take a look at. While they dont have self serve, the minimums are easy to clear and the geo location targeting is verified (since Nextdoor sends a postcard to activate)

I think the obvious answer is Facebook -- it's hard to imagine any other channel coming close to matching the effectiveness of Facebook for local targeting. 

Snapchat is another option: you can geofence an on-demand filter with Snapchat using a map, which is pretty cool and obviously very specific. Snap filters are great if you want to target a big sports game or conference or event with a large concentration of people where the geographic boundaries matter. More info here.

TV can work for local advertising but you need to carefully manage the placements via the local affiliate / station, which can be super time consuming, and you get very little data to go on regarding demographic reach. I've never had any success with radio -- it doesn't feel like a viable channel for digital products to me.

Based on my experience, FB is the most relevant digital channel.
However, depending on your business, for city targeting, you might consider good old tradional offline channels like OOH, radio or local TVs.

This doesn't directly answer your question, but is a tactic I've seen some do. You can use a hyperlocal dmp provider to build audiences that the generic traffic providers will let you target.