Azure Searching Metadata in blobs

Although still in preview, with Blob Index, you can now do a query search on blob metadata (tags).

You won't need to loop thru all of your blobs until you find what you're looking for.

Here's a snippet from the full article:

Blob Index—a managed secondary index, allowing you to store multi-dimensional object attributes to describe your data objects for Azure Blob storage—is now available in preview. Built on top of blob storage, Blob Index offers consistent reliability, availability, and performance for all your workloads. Blob Index provides native object management and filtering capabilities, which allows you to categorize and find data based on attribute tags set on the data.

The accepted answer is highly inefficient, looping through and loading every single Blob and their associated Metadata to check for values wouldn't perform very well with any reasonable volume of data.

It is possible to search Blob meta data using Azure Search. A search index can be created that includes Blobs custom meta data.

The following comprehensive articles explain it all:

Indexing Documents in Azure Blob Storage with Azure Search
Searching Blob storage with Azure Search