How can I find apps for old ipods touch (4.2.1)?

See Kappy's chart to see if your model can be updated…

how do i upgrade my ipod touch 4.2.1 to a higher level plz help

You can try using a 'google hack' to search the store for compatible apps if you are stuck on 4. Enter this next line into google.com's search field.

site:itunes.apple.com/us/ "requires ios 2.0|2.1|2.2|3.0|3.1|3.2|4.0|4.1|4.2"

Older devices are limited in terms of CPU, RAM & sensors, so many newer apps will not work.

Post feedback to Apple suggesting how they could improve the store (they could add filtering by iOS version for a start).

http://www.apple.com/feedback

To more easily find compatible apps:

iOSSearch - search the iTunes store for compatible apps.

Apple Club - filter apps by iOS version.

Starting when iOS 7 was released, Apple now allows downloading the last compatible version of some apps (iOS 4.2.1 and later only)

App Store: Downloading Older Versions of Apps on iOS - Apple Club

App Store: Install the latest compatible version of an app

You first have to download the non-compatible version on your computer. Then when you try to purchase the version on your iPod you will be offered a compatible version if one exists.

'Last Compatible' Version of Apps for Users Running Legacy Versions of iOS - Mac Rumors

Dybento wrote:

Apple must be kidding us...How on earth can´t I find apps for my older version of iPod touch (4.2.1)? What should I do? Throw it away? Simply ridiculous!!!

The second generation iPod (which is what I assume you have) was released in 2008. You should expect it to be outdated by now.

The article below may help.

Install the latest compatible version of an app on an earlier version of iOS or OS X - Apple Support