According to TSA.gov , the FAQ says no : I’m traveling with my family; can they also use the TSA Pre✓ ® lane?
Family members ages 12 and under traveling with an eligible parent or guardian with a TSA Pre✓ ® indicator on their boarding pass can participate in expedited screening.
Family members 13 and older must go through standard security lanes or should apply for a DHS trusted traveler program.
I know your question isn't about family, but 'travel companions', but seeing as they don't even allow family members over 13 to join you on your KTN, it can safely be assumed by a reasonable person (and yes, I know we're talking TSA here, irony noted) that a non-family member would also not be eligible to travel under your KTN.
travel.stackexchange.com/users/16725/CGCampbell
My sister and I both have KTNs and recently traveled with a friend, booked together in one record.
She doesn't have a KTN but received TSA pre-check on both legs of the journey.
Two friends who booked independently did not.
So it seems that there is a higher likelihood of the TSA pre going to some traveling on the same record as another KTN holder.
travel.stackexchange.com/users/57715/greentravelgal
I have a KTN #.
My wife does not and is not even a U.S. Citizen but always gets TSA Pre Check when traveling with me on Delta, American and United.
Southwest is the exception whereas I get Pre Check
but she has to go through regular line.
So far, 100 % of the time this is the case.
Even when she didn't have her permanent resident card, she still had TSA Pre Check.
It makes no sense to me.
I am not complaining, just confused why she gets cleared for TSA Pre.
travel.stackexchange.com/users/50257/Dave
I have a Global Entry card, which allows for TSA Pre access, but only on UAL, not Frontier or Southwest.
My wife has never applied but generally gets TSA Pre on her UAL boarding pass also when we book and fly together.
Go figure.
travel.stackexchange.com/users/43539/Mort Frequentflyer
Officially, Known Traveler Numbers (KTNs) belong to a person, so every traveler needs their own KTN so long as they are 13 or older.
Anecdotally, I have KTN and my partner does not.
I have made three roundtrip flights over the last six months (domestic) and we both receive precheck on our tickets.
As others have reported, some travelers have been admitted to the precheck line simply by asking nicely.
travel.stackexchange.com/users/40319/Brian R
If I have  TSA PreCheck  (i.e. I have a KTN from TSA and the "pre-check" logo gets printed on my boarding pass) and a travel companion does not, can they go with me through the PreCheck security lines? This is assuming that the travel companion is booked in the same reservation on the same flights and is also a U.S. citizen and not on any no-fly or otherwise increased scrutiny lists.  I'm guessing the answer is no, but I haven't seen anything from TSA specifically addressing this.
Can others in my party go through TSA PreCheck?
travel.stackexchange.com
<airport-security><tsa><tsa-precheck><trusted-traveler>
travel.stackexchange.com/questions/56938
travel.stackexchange.com/users/12011/reirab
Family members ages 12 and under traveling with an eligible parent or guardian with a TSA Pre✓ ®  indicator on their boarding pass can participate in expedited screening, but older children and presumably also non-family members would not be eligible. Children aged 12 and under travelling with an eligible parent or guardian with a TSA pre check indicator on their boarding pass can pass through expedited screening. Everybody else must pass through normal screening.
Children aged 12 and under travelling with an eligible parent or guardian with a TSA pre check indicator on their boarding pass can pass through expedited screening. Everybody else must pass through normal screening.