Is stealing a verb

Yes, the Word 'stealing' is a verb, the present participle, present tense of the verb to 'steal'.

The present participle of the verb also functions as an adjective and a gerund (a verbal noun).

Examples:

The fraud was stealing their money with a smile on his face. (verb)

She caught him stealing in at three in the morning. (verb)

He got a stiff prison sentence, his stealing days are over. (adjective)

Stealing comes in many forms and some aren't easily recognized. (noun, subject of the sentence)