All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
It is impermissible to accuse someone of theft without proof or strong circumstantial evidence. The basic principle is that the person who is accused of theft in the absence of proof is innocent. It is prohibited to accuse him and mistrust him without a valid reason. Allah, The Exalted, says (what means): {O you who have believed, avoid much (negative) assumption. Indeed, some assumption is sin.} [Quran 49:12] The Prophet, sallallahu ‘alayhi wa sallam, said, “Beware of suspicion, for suspicion amounts to the worst form of lying.” [Al-Bukhaari and Muslim]
Hence, if you have strong circumstantial evidence proving that this worker has stolen your tablet and accordingly you accused him of this crime and informed your father of it, there is no harm on you or on your father in what he did. You can refer the case to the concerned authorities to give you your due right, and you are also entitled to refrain from reporting the incident if you wish. However, if the circumstantial evidence is weak, then accusing him is mere negative assumption and a lie against him, and it is impermissible for you and your father to accuse him of theft.
Allah knows best.