I am a filipino with a US tourist visa. If I come to London first, can I go to US from there?
Yes, you can. The US will not care at all from where you enter the country.
While some countries issue certain visas that may require you to enter a country on a certain border crossing or coming from a certain country, this is not very common and will certainly be stated on the visa. If it does not say anything about this, there are no restrictions.