Ruling on telling the authorities about one who is stealing
Question

                I work in a private company and some workers steal things before my eyes, and I keep quiet about this. 

My question is: Is there any sin on me for this?.
Praise be to Allah.
    It is proven in Saheeh Muslim (49) that Abu Sa’eed 
    al-Khudri (may Allaah be pleased with him) said: I heard the Messenger of 
    Allaah  (peace and blessings of Allaah be upon him) say: “Whoever among 
    you sees an evil action, let him change it with his hand (by taking action); 
    if he cannot, then with his tongue (by speaking out); and if he cannot, then 
    with his heart (by hating it and feeling it is wrong), and that is the 
    weakest of faith.” 

    Al-Nawawi (may Allaah have mercy on him) said: 

    With regard to the words of the Prophet  (peace and 
    blessings of Allaah be upon him) “let him change it”, this is a command in 
    the sense that it is obligatory according to the consensus of the ummah. 
    Enjoining what is good and forbidding what is evil is an obligation 
    according to Qur’aan and Sunnah and the consensus of the ummah, and it is 
    also part of the sincerity (naseehah) that is the faith. End quote. 

    Sharh Saheeh Muslim (2/22) 

    The Children of Israel would see evil but keep silent and not 
    denounce it, and that silence caused them to be cursed, as Allaah, may He be 
    glorified, says (interpretation of the meaning): 

    “Those among the Children of Israel who disbelieved were 
    cursed by the tongue of Dawood (David) and ‘Eesa (Jesus), son of Maryam 
    (Mary). That was because they disobeyed (Allaah and the Messengers) and were 
    ever transgressing beyond bounds.

    79. They used not to forbid one another from Al-Munkar 
    (wrong, evildoing, sins, polytheism, disbelief) which they committed. Vile 
    indeed was what they used to do”

    [al-Maa’idah 5:78-79]  

    Based on that, it is not permissible for the one who sees an 
    evil to keep quiet about it when he is able to denounce it and change it. He 
    should start with changing it with his hand (by taking action) if he is able 
    to do that, such as if he is responsible for the one who is doing the evil 
    and has some authority over him. If he cannot change it with his hand, then 
    he should denounce it with his tongue (by speaking out), by enjoining what 
    is good and forbidding what is evil, and by advising in the way that is 
    best. Denouncing it verbally also includes telling those who are able to put 
    a stop to this evil, and he must try hard to do that. If he is unable to do 
    that, then he can avoid sin by denouncing it in his heart. If he falls short 
    in denouncing the evil in the way that he is able to, then he will be a 
    partner in sin with the sinner. 

    If he has tried his best and done his duty of enjoining what 
    is good and forbidding what is evil, and the sinner does not respond, there 
    is no sin on him, because Allaah says (interpretation of the meaning): 

    “O you who believe! Take care of your ownselves. If you 
    follow the (right) guidance [and enjoin what is right (Islamic Monotheism 
    and all that Islam orders one to do) and forbid what is wrong (polytheism, 
    disbelief and all that Islam has forbidden)] no hurt can come to you from 
    those who are in error. The return of you all is to Allaah, then He will 
    inform you about (all) that which you used to do”

    [al-Maa’idah 5:103].

    Shaykh al-Shanqeeti (may Allaah have mercy on him) said: 

    The one who denounces evil according to his ability is safe 
    from this sin, but the one who approves of it and keeps quiet about it is a 
    sinner like the one who does it. End quote. 

    Adwa’ al-Bayaan (1/467). 

    You have to advise these people, first of all, to fear Allaah 
    and to refrain from stealing the property of others, and they have to return 
    what they took previously. If they refrain, then you will have done the 
    right thing towards them and the owner of the property. But if they persist 
    in what they are doing, then you must inform those who can put a stop to 
    what they are doing, even if you tell the owner of the property himself. It 
    is not essential for you to make it known that you are the one who is 
    telling on them, rather it is sufficient to send a letter – for example – to 
    the owner of the property and tell him what is really going on. It is 
    preferable for it to be accompanied by documents that prove that what you 
    are saying is true, so that he will take the matter seriously. Thus you will 
    have fulfilled your duty and saved yourself from sin.