You send the link to the NYPD...let us say you are out and you happen to see him, last time you had no idea he was around but this time you spot him and he has a big lens -- maybe he got a photo of you without your knowledge maybe he did not -- you immediately email people in "your safety network" -- if you don't have email capacity make sure you note the time, place and tell as many people as possible. If the stalker posts it in a place you can see it -- take the link but also capture the page on email people in your safety network.
The same for online stalking which can be done in many different ways and the more people you make part of your safety network the better...if possible law enforcement, check with the internet for resources, lawyers, the laws on cyber stalking are changing and the seriousness being recognized so flesh or internet...create a safety network and keep a record. Ask the police if they have a list of resources to direct. Look on the internet as well for resources.
Contact any resources, legal departments, flag etc. If you ask someone to please leave you alone and they don't that is something to be concerned about and reach out to your safety network. Make sure to contact the NYPD and ask them as many questions as possible to understand the law and what are rights to basic safety and try to expand your safety network and your resources as much as possible.
