Create Crawled Property for Custom Column - SharePoint 2013

Create Site column "TestName" using following powershell script 

#Get site and web object

$site = Get-SPSite -Identity "http://MySiteurl"

$web = $site.RootWeb

#Assign fieldXML variable with XML string for site column

$fieldXML = '<Field Type="Text"

Name="TestName"

Description="This is a test date column."

DisplayName="Test Name"

StaticName="TestName"

Group="Test Custom Columns"

Hidden="FALSE"

Required="FALSE"

Sealed="FALSE"

ShowInDisplayForm="TRUE"

ShowInEditForm="TRUE"

ShowInListSettings="TRUE"

ShowInNewForm="TRUE"></Field>'

#Output XML to console

write-host $fieldXML

#Create site column from XML string

$web.Fields.AddFieldAsXml($fieldXML)

#Example of changing the site column settings after creation

#Configure Test Date column to be Date Only instead of Date & Time

$dtField = $web.Fields["Test Name"]

$dtField.Update()

#Dispose of Web and Site objects

$web.Dispose()

$site.Dispose()

Open  Search Service application  in central admin and run incremental crawl. 

Under Crawled properties search for "TestName"

If missing custom site columns in crawled properties, you should:

1. verify your custom fields is in use (in existing item or at least associated with visible content type)
2. check your search settings and crawled category properties
3. do a Search Index Reset
4. perform a full crawl

Even after full crawl if you can't find your column in crawled properties then create it using following powershell script.

add-pssnapin microsoft.sharepoint.powershell

$searchapp = Get-SPEnterpriseSearchServiceApplication

$cat = Get-SPEnterpriseSearchMetadataCategory -SearchApplication $searchapp -Identity SharePoint

$crawlprop = Get-SPEnterpriseSearchMetadataCrawledProperty -SearchApplication $searchapp -Category $cat -Limit 1

New-SPEnterpriseSearchMetadataCrawledProperty -SearchApplication $searchapp -Name "ows_TestName" -PropSet $crawlprop.PropSet -Category $crawlprop.CategoryName -IsNameEnum $false -VariantType $crawlprop.VariantType -IsMappedToContents $false

Now search again in crawled properties. you will find your "TestName" column.