How do I deal with people harrassing me but I dont know who it is?

Firstly make sure you are not suffering paranoia.

You say you can not point your finger at them which does raise the question of possible mental health issues. Are you absolutely sure this is happening? Is it possible you may be reading ordinary unfortunate events as being deliberately targeted at you?

But…. if there is clear evidence that people are definitely targeting you for an anonymous campaign of harassment then the first thing you would need to do is identify them and collect evidence.

If this were happening to me I would use technology to achieve this:

Video recording
Audio recording
Motion sensors

If there are patterns to the harassment ie;

things always happen at certain times or in certain places then your job will be easier. This obviously provides opportunity for reliable analysis.

If the harassment is in the form of unpredictable random occurrences then things do become more difficult. In this case you would have to put on your Sherlock Holmes hat. Conduct an investigation as far as you can to identify the perpetrator or perpetrators.

Things to consider:

Motive. Who might have a motive to target you? Have you had any run ins with anyone that might have created resentments to head your way? Are you in a relationship that may have created jealousy in someone? Think about events in your life just prior to when this all started. Can you identify any interactions or events that may raise concerns?
Opportunity. If you do suspect particular persons, try to establish opportunity. Was the person in a position to achieve the events that took place against you. Is there any way to verify the person’s whereabouts or activities at the time of harassment taking place against you?
Body language of people around you. Do you have an instinct about anyone who may not be coming across normal in terms of their body language toward you? Is there anyone you interact with who avoids eye contact, doesn’t smile, is dismissive of you? Reacts negatively to things you say? Maybe you can become aware of persons who seem to notice you when you arrive places and are taking an interest in you from a distance?
Witness testimony. If you do have suspicions of certain people then are there any friends or associates who mix with them ? Could you maybe provoke conversation with them that might reveal how these people feel about you. Have they said anything in conversation about you? Ask subtlety, be clever, don’t make it too obvious what you are doing.

Once your investigations are complete then hopefully you will have a better idea of what is happening.

How to deal with it.

Once you have a good idea of who is targeting you then the first thing to consider is how serious this is.

Are they breaking the law? Is this campaign a strong personal vendetta that you fear may escalate? If so then you may need to inform the police.

If the harassment is more of an annoyance and not really that serious in terms of the law, then it would be a good idea to try to discover what is driving the person or persons against you.

The first rule of any relationship in business or personal is “take care of concerns”

If someone has concerns in regards to you then this is something you must address. As long as those concerns are present you will have a critic working against you or even an enemy going further to effect you.

Talk to the person and tell them calmly and maturely that you know they have been engineering events against you. Ask them calmly why they are doing this. Have you offended them in some way. Tell them that if this is the case you would really like to address that because you don’t like the idea that you may have offended someone. Ask what can you do to fix things? If you need to make any kind of apology then do that. We can all accidentally offend people and not even realise it. It may turn out that the person just doesn’t like your personality. f this is the case then try to discover what aspect of your attitude is causing issues. If one person has turned on you because of this then more could easily do the same.