This is an issue that you should call 911 about when its happening. See Click Fix or 311 can't do much about this. This site and 311 are for complaints related to city services. Anything else should be directed at 911.

Doesn't seem right to me to tie up 911 for this - maybe if I call or email the 17th precinct they could send out the bike patrol. Anyone know their phone number? This happens several times during the weekends when I see it and probably during the weekdays when I'm at work. Does anyone have any other suggestions? Thanks - I'll mark this as closed

Its not tying up 911. Its their job and the police have requested at every PSA meeting (3rd Thursday of the month at the church on 19th street) and at the community meetings that they want complaints like this to go through 911. The dispatchers have a system for prioritizing 911 calls. So if there is something more important that needs attention, it will get moved to the bottom of the list and addressed as soon as its possible. The bike patrols are on the same dispatch system as the officers in cars. If you call the precinct, they will likely tell you to call 911.
Again, you have to call when its happening, or there really isn't anything they can do about it.