I have a 2010 VW Beetle. I did not use my car during the Christmas holiday and when I came back home I got 4 flat tires. Then I had it towed to the mechanic but they said they didn’t find any leaks or punctures in any of the tires and it was just because the freezing cold weather. After 2 weeks I had flat tires again and I went to another mechanic, they told me the same thing but a few days later the low tire pressure light keeps showing on the dashboard and the tires become pretty flat every other day (about 15psi). This is really bothering me because I have to go to the gas station to put air in the tire everyday. Does anyone know what I can do?
Have them clean and reseal the the tire beads on the rim and replace the valve stems would be my first thought.
You have a leak. My car was under repair for several weeks and did not lose air. Having to add air everyday to keep the TPMS light off means you are leaking air somewhere. Could be at the rim or at the valves, but air is escaping somehow.
Do you have chrome rims?
Are those the original tires? Or did you recently get new ones? If someone put those on fairly recently than I’d say to take it back to them. For this to happen on all 4 tires indicates the same kind of systematic problem. Either way, you’ll need to have all 4 remounted and balanced. If you’re soon to be due for new tires, you might just think about that. I’d make sure that it is a local tire shop with a good reputation as someone who knows what they are doing should probably be inspecting everything.
Are all of your tires going low? If you have to air them up every day then you have a leak(s) that should be easy to find or someone is tampering with your car.
Mix up a spray bottle of soapy water and spray it on your tires, especially the valve and bead areas. With a leak this bad, chances are that you’ll see bubbles pretty quickly where the leak is.
Driving on tires that are at 15 PSI is not a good thing to do. You can damage the sidewalls and make the tires unsafe to use.
Could also submerge the tires in a large tub of water and look for bubbles
I agree with the answers already posted here and will say this: The probability of all 4 tires having leaks is nearly impossible. I think someone is messing with your tires.
Consider that the wheels themselves may be a bit porous made worse by the cold. It would be strange for all 4 to do this suddenly at the same time but they were manufactured about the same time so, maybe. Consider the previous comments from @cigroller about new tires and @missileman about a prankster first.
I’ll go off-topic here. But there’s something about tires in this story
Years ago, during my apprenticeship, the overwhelming majority of the kids were from very rough areas, and didn’t care for school at all. They always wanted to play hookie after lunch. Geniuses that they were, they figured if anybody every asked why they didn’t show up after lunch, they’d all say “Mr. such and such said to take the rest of the day off.”
Well, the problem was that the story would never have held up, for various reasons
Unlike the rest of the bozos, who were always telling the teachers to f . . k off, shove it up yours, etc., I actually wanted to learn something. Because I realized this was literally my last chance to make something of myself. I had already flunked out of college for goofing off, so I was already a few years older than most of the kids. I had barely gotten in, because of my age, and I fully well realized there wouldn’t be any more chances, if I blew this.
I told the other kids “Come on guys, you know this isn’t going to work. The story will never hold up”
Since they realized that if even one student showed up after lunch (me), the story wouldn’t hold up, they grudgingly returned to classes after lunch.
But they did take their revenge by letting the air out of my tires. Thankfully, they just depressed the valve cores. They didn’t actually remove them.
Out of that batch, an extremely large percentage didn’t make it to the end of the apprenticeship . . . got thrown out, quit, got pregnant, became drug dealers, etc. . . . or didn’t pass final exams at the end. One particular guy didn’t pass the written portion of the exam. He was given 2 more chances, and he failed them both, all because he was too cool to study.
Thank you all for your thoughts and suggestions! 
I cannot make any recommendations because I know little about the subject, but a quick internet search showed home security camera systems for under $100 and sophisticated basic (one camera) home systems for not much more. One of these might get to the root of the problem.